Minor cleanup

Author: SimenB

.travis.yml

@@ -1,3 +1,2 @@
 language: node_js
 node_js: node
-

addAssetHtmlPlugin.js

@@ -14,7 +14,7 @@ function resolvePublicPath(compilation, filename, publicPath) {
   }
 
   if (resolvedPublicPath.length && resolvedPublicPath.substr(-1, 1) !== '/') {
-    resolvedPublicPath += '/';
+    resolvedPublicPath = `${resolvedPublicPath}/`;
   }
   return resolvedPublicPath;
 }