fix(middleware): Use forEach in karma.js

Use `forEach` instead of `for..in` as it's better
practices and fix karma-runner#2671.

lib/middleware/karma.js

@@ -174,15 +174,10 @@ var createKarmaMiddleware = function (
 
           var scriptTags = []
           var scriptUrls = []
-          for (var i in files.included) {
-            var file = files.included[i]
+          files.included.forEach(function (file) {
             var filePath = file.path
             var fileExt = path.extname(filePath)
 
-            if (!files.included.hasOwnProperty(i)) {
-              continue
-            }
-
             if (!file.isUrl) {
               filePath = filePathToUrlPath(filePath, basePath, urlRoot, proxyPath)
 
@@ -195,12 +190,12 @@ var createKarmaMiddleware = function (
 
             if (fileExt === '.css') {
               scriptTags.push(util.format(LINK_TAG_CSS, filePath))
-              continue
+              return
             }
 
             if (fileExt === '.html') {
               scriptTags.push(util.format(LINK_TAG_HTML, filePath))
-              continue
+              return
             }
 
             // The script tag to be placed
@@ -213,7 +208,7 @@ var createKarmaMiddleware = function (
 
             var crossOriginAttribute = includeCrossOriginAttribute ? CROSSORIGIN_ATTRIBUTE : ''
             scriptTags.push(util.format(SCRIPT_TAG, scriptType, filePath, crossOriginAttribute))
-          }
+          })
 
           // TODO(vojta): don't compute if it's not in the template
           var mappings = files.served.map(function (file) {