feat(watcher): ignore initial "add" events

Initially all the patterns are scanned using glob. Then we start watching then
with chokidar. Chokidar now allows to ignore initial "add" event, which was
ignored by the fileList anyway.

lib/watcher.js

@@ -75,6 +75,7 @@ exports.watch = function(patterns, excludes, fileList) {
   var watchedPatterns = getWatchedPatterns(patterns);
   var options = {
     ignorePermissionErrors: true,
+    ignoreInitial: true,
     ignored: createIgnore(watchedPatterns, excludes)
   };
   var chokidarWatcher = new chokidar.FSWatcher(options);