feat: Let the ApolloQuery be a renderless component if tag prop is undefined (#365)

* Let the ApolloQuery be a renderless component if `tag` prop is undefined

* Let the ApolloMutation component be a renderless component if `tag` prop is undefined

src/components/ApolloMutation.js

@@ -81,6 +81,6 @@ export default {
     } else {
       result = [result].concat(this.$slots.default)
     }
-    return h(this.tag, result)
+    return this.tag ? h(this.tag, result) : result
   },
 }

src/components/ApolloQuery.js

@@ -192,6 +192,6 @@ export default {
     } else {
       result = [result].concat(this.$slots.default)
     }
-    return h(this.tag, result)
+    return this.tag ? h(this.tag, result) : result
   },
 }