vim: Fix invalid import in gn-format.py

Broken at 12f53f06554d665c82160d4edeab0200a37081f8. I swear I tried
this, but I must have confused myself by not re-source'ing something.

(from __future__ imports have to go at the top of the file before other
imports.)

Change-Id: I23c56ca7a21dbf83469e92834828ea4557dd6696
Reviewed-on: https://gn-review.googlesource.com/c/gn/+/7260
Commit-Queue: Nico Weber <thakis@chromium.org>
Reviewed-by: Nico Weber <thakis@chromium.org>

misc/vim/gn-format.py

diff --git a/misc/vim/gn-format.py b/misc/vim/gn-format.py
index f21f1b9..d292e6d 100644
--- a/misc/vim/gn-format.py
+++ b/misc/vim/gn-format.py
@@ -14,11 +14,11 @@
 # be used. It operates on the current, potentially unsaved buffer and does not
 # create or save any files. To revert a formatting, just undo.
 
+from __future__ import print_function
 import difflib
 import subprocess
 import sys
 import vim
-from __future__ import print_function
 
 # Change this to the full path if gn is not on the path.
 binary = 'gn'