plugin.py: tiny fix so that it works with newer gEdit

Author: Ildar Mulyukov

Diff for: sourcecodebrowser/plugin.py

@@ -3,6 +3,7 @@
 import logging
 import tempfile
 from . import ctags
+import gi
 from gi.repository import GObject, GdkPixbuf, Gedit, Gtk, PeasGtk, Gio
 
 try: