fix(config): #1113 Watching is not working properly on linux

Solve bug in watch service by using pooling

Closes #1113

lib/config.js

@@ -212,7 +212,7 @@ var Config = function() {
   this.colors = true;
   this.autoWatch = true;
   this.autoWatchBatchDelay = 250;
-  this.usePolling = process.platform === 'darwin';
+  this.usePolling = process.platform === 'darwin' || process.platform === 'linux';
   this.reporters = ['progress'];
   this.singleRun = false;
   this.browsers = [];