tools: use 'from io import StringIO' in ninja.py

PR-URL: #29371
Reviewed-By: Ben Noordhuis <[email protected]>
Reviewed-By: Jiawen Geng <[email protected]>
Reviewed-By: Richard Lau <[email protected]>
Reviewed-By: Luigi Pinca <[email protected]>

Author: cclauss

tools/gyp/pylib/gyp/generator/ninja.py

@@ -20,7 +20,7 @@
 import gyp.msvs_emulation
 import gyp.MSVSUtil as MSVSUtil
 import gyp.xcode_emulation
-from cStringIO import StringIO
+from io import StringIO
 
 from gyp.common import GetEnvironFallback
 import gyp.ninja_syntax as ninja_syntax