Postpone plugin invokation in on_modified event

If plugin in on_modified event takes more than 0.02 sec user gets a
warning. This commit makes plugin actually do its job in next event
loop cycle.

git_gutter_events.py

@@ -1,3 +1,4 @@
+import sublime
 import sublime_plugin
 from view_collection import ViewCollection
 
@@ -8,7 +9,11 @@ def on_load(self, view):
 
     def on_modified(self, view):
         if view.settings().get('git_gutter_live_mode', True):
-            ViewCollection.add(view)
+            # Sublime Text is very strict on the amount of time plugin
+            # uses in performance-critical events. Sometimes invoking plugin
+            # from this event causes Sublime warning to appear, so we need to
+            # schedule its run for future.
+            sublime.set_timeout(lambda: ViewCollection.add(view), 1)
 
     def on_clone(self, view):
         ViewCollection.add(view)