Update code coverage output location

Remove one layer of dir traversal after moving karma.config.js from
src/scripts to src/sidebar.

src/karma.config.js

@@ -87,7 +87,7 @@ module.exports = function(config) {
     },
 
     coverageReporter: {
-      dir: '../../coverage/',
+      dir: '../coverage/',
       reporters: [
         {type:'html'},
         {type:'json', subdir: './'},