build: trivial style fix

setup.py

@@ -28,7 +28,7 @@ def get_version():
         with open('VERSION', 'r') as v:
             return v.read()
     if os.path.exists('.git'):
-        p = subprocess.Popen(['git','describe','--dirty=.dirty','--match=v*'],
+        p = subprocess.Popen(['git', 'describe', '--dirty=.dirty', '--match=v*'],
                 stdout=subprocess.PIPE, stderr=subprocess.PIPE)
         result = p.communicate()[0]
         if p.returncode == 0: