app: Migrate the overlooked versions.length to num_versions (#10616)

Author: eth3lbert

app/templates/crate/version.hbs

@@ -74,7 +74,7 @@
     <div local-class='stat'>
       <span local-class="num">
         {{svg-jar "crate"}}
-        <span local-class="num__align">{{ this.crate.versions.length }}</span>
+        <span local-class="num__align">{{ this.crate.num_versions }}</span>
       </span>
       <span local-class="stat-description">Versions published</span>
     </div>