docs(slots): Update docs with correct v-slot syntax

Author: mattelen

documentation/src/components/example-code/OptionGroups.vue

@@ -1,7 +1,7 @@
 <template>
   <div><label class="typo__label">Groups</label>
     <multiselect v-model="value" :options="options" :multiple="true" group-values="libs" group-label="language"
-                 :group-select="true" placeholder="Type to search" track-by="name" label="name"><span slot="noResult">Oops! No elements found. Consider changing the search query.</span>
+                 :group-select="true" placeholder="Type to search" track-by="name" label="name"><template v-slot:noResult>Oops! No elements found. Consider changing the search query.</template>
     </multiselect>
     <pre class="language-json"><code>{{ value }}</code></pre>
   </div>