CN-1377 国际化内容补充:1.检查下拉框，去掉placeholder;

src/components/rightBox/settings/I18nBox.vue

@@ -26,7 +26,7 @@
                        class="right-box__select"
                        clearable
                        collapse-tags
-                       placeholder=""
+                       placeholder=" "
                        popper-class="right-box-select-dropdown prevent-clickoutside"
                        size="small"
                        @change="()=>{ this.$forceUpdate() }">

src/components/rightBox/settings/UserBox.vue

@@ -45,7 +45,7 @@
                        class="right-box__select"
                        clearable
                        collapse-tags
-                       placeholder=""
+                       placeholder=" "
                        popper-class="right-box-select-dropdown prevent-clickoutside"
                        size="small"
                        @change="()=>{ this.$forceUpdate() }">
@@ -61,7 +61,7 @@
                        class="right-box__select"
                        clearable
                        collapse-tags
-                       placeholder=""
+                       placeholder=" "
                        popper-class="right-box-select-dropdown prevent-clickoutside"
                        size="small">
               <template v-for="lang in langData" :key="lang.value">
@@ -76,7 +76,7 @@
                        class="right-box__select"
                        clearable
                        collapse-tags
-                       placeholder=""
+                       placeholder=" "
                        popper-class="right-box-select-dropdown prevent-clickoutside"
                        size="small">
               <template v-for="theme in themeData" :key="theme.value">

src/views/charts/ChartHeader.vue

@@ -58,7 +58,7 @@
             size="mini"
             v-model="table.limit"
             class="option__select select-topn"
-            placeholder=""
+            placeholder=" "
             popper-class="option-popper"
             @change="tableLimitChange"
           >
@@ -125,7 +125,7 @@
             size="mini"
             v-model="copyOrderPieTable"
             class="option__select select-column"
-            placeholder=""
+            placeholder=" "
             popper-class="option-popper"
             @change="orderPieTableChange"
           >

src/views/charts2/Panel.vue

@@ -24,7 +24,7 @@
         <el-select
             size="mini"
             v-model="metric"
-            placeholder=""
+            placeholder=" "
             popper-class="common-select"
             v-if="showMetric"
             :popper-append-to-body="false"

src/views/charts2/charts/dnsInsight/DnsTrafficLine.vue

@@ -33,6 +33,7 @@
             <el-select
                 size="mini"
                 v-model="lineMetric"
+                placeholder=" "
                 popper-class="common-select"
                 :popper-append-to-body="false"
                 @change="metricSelectChange"
@@ -47,6 +48,7 @@
             <el-select
                 size="mini"
                 v-model="lineRefer"
+                placeholder=" "
                 :disabled="!lineTab"
                 popper-class="common-select"
                 :popper-append-to-body="false"

src/views/charts2/charts/entityDetail/EntityDetailLine.vue

@@ -50,7 +50,7 @@
               <el-select
                   size="mini"
                   v-model="metric"
-                  placeholder=""
+                  placeholder=" "
                   popper-class="common-select"
                   :popper-append-to-body="false"
                   @change="metricChange"
@@ -66,6 +66,7 @@
                   size="mini"
                   v-model="lineRefer"
                   :disabled="!lineTab"
+                  placeholder=" "
                   popper-class="common-select"
                   :popper-append-to-body="false"
                   @change="referenceSelectChange"

src/views/charts2/charts/linkMonitor/LinkTrafficLine.vue

@@ -42,6 +42,7 @@
              <el-select
                  size="mini"
                  v-model="lineMetric"
+                 placeholder=" "
                  popper-class="common-select"
                  :popper-append-to-body="false"
                  @change="metricSelectChange"

src/views/charts2/charts/networkOverview/NetworkOverviewLine.vue

@@ -38,6 +38,7 @@
                 size="mini"
                 v-model="lineRefer"
                 :disabled="!lineTab"
+                placeholder=" "
                 popper-class="common-select"
                 :popper-append-to-body="false"
                 @change="referenceSelectChange"

src/views/charts2/charts/npm/NpmMap.vue

@@ -9,6 +9,7 @@
           v-model="trafficDirection"
           class="map-select map-select__direction"
           popper-class="map-select-down"
+          placeholder=" "
           :popper-append-to-body="false"
       >
         <el-option value="Server">Server</el-option>

src/views/charts2/charts/npm/NpmTrafficLine.vue

@@ -8,7 +8,7 @@
           <el-select
               size="mini"
               v-model="metricFilter"
-              placeholder=""
+              placeholder=" "
               popper-class="common-select"
               :popper-append-to-body="false"
               @change="metricChange"