fix: don't concatenate ignore regexes

The initial `ignored` may be undefined. If it isn't then a pipe character should
be inserted. This is all unnecessary though if we build up an array like before
4826c87.

lib/monitor/watch.js

@@ -46,7 +46,7 @@ function watch() {
 
       // don't ignore dotfiles if explicitly watched.
       if (!dir.match(dotFilePattern)) {
-        ignored = new RegExp(ignored.source + dotFilePattern.source);
+        ignored = [ignored, dotFilePattern];
       }
 
       var watcher = chokidar.watch(dir, {