docs: fix deprecated scoped slot syntax

Author: yyx990803

docs/en/features/es2015.md

@@ -48,7 +48,7 @@ can be simplified to:
 
 ``` html
 <my-component>
-  <template scope="{ id, text }">
+  <template slot-scope="{ id, text }">
     <span>{{ id }} {{ text }}</span>
   </template>
 </my-component>

docs/ja/features/es2015.md

@@ -47,7 +47,7 @@ export default {
 
 ``` html
 <my-component>
-  <template scope="{ id, text }">
+  <template slot-scope="{ id, text }">
     <span>{{ id }} {{ text }}</span>
   </template>
 </my-component>

docs/kr/features/es2015.md

@@ -48,7 +48,7 @@ export default {
 
 ``` html
 <my-component>
-  <template scope="{ id, text }">
+  <template slot-scope="{ id, text }">
     <span>{{ id }} {{ text }}</span>
   </template>
 </my-component>

docs/pt_BR/features/es2015.md

@@ -48,7 +48,7 @@ Pode ser simplificado para:
 
 ```html
 <my-component>
-  <template scope="{ id, text }">
+  <template slot-scope="{ id, text }">
     <span>{{ id }} {{ text }}</span>
   </template>
 </my-component>

docs/ru/features/es2015.md

@@ -48,7 +48,7 @@ export default {
 
 ``` html
 <my-component>
-  <template scope="{ id, text }">
+  <template slot-scope="{ id, text }">
     <span>{{ id }} {{ text }}</span>
   </template>
 </my-component>