widgets.main: rename "Browser" menu action to "File Browser"

Closes #269

Suggested-by: Ｖ字龍(Vdragon) <pika1021@gmail.com>
Signed-off-by: David Aguilar <davvid@gmail.com>

cola/widgets/main.py

@@ -276,7 +276,7 @@ def __init__(self, model, parent=None, settings=None):
                 N_('Review...'), guicmds.review_branch)
 
         self.browse_action = add_action(self,
-                N_('Browser...'), worktree_browser)
+                N_('File Browser...'), worktree_browser)
         self.browse_action.setIcon(qtutils.git_icon())
 
         self.dag_action = add_action(self, N_('DAG...'), self.git_dag)