build: enable ninja.py it import StringIO on Python 3

This change supports access to StringIO on both Python 2 and Python 3

Author: cclauss

gyp/pylib/gyp/generator/ninja.py

@@ -19,7 +19,10 @@
 import gyp.msvs_emulation
 import gyp.MSVSUtil as MSVSUtil
 import gyp.xcode_emulation
-from cStringIO import StringIO
+try:
+  from cStringIO import StringIO
+except ImportError:
+  from io import StringIO
 
 from gyp.common import GetEnvironFallback
 import gyp.ninja_syntax as ninja_syntax