Change default generators on windows to include msvs-ninja rather than msvs

gyp_skia

Index: gyp_skia
diff --git a/gyp_skia b/gyp_skia
index 66adf08cb90b465b680533857a6acb71910d665c..435e61c18a9791d268fcf54514b2b776f3b09b41 100755
--- a/gyp_skia
+++ b/gyp_skia
@@ -84,9 +84,9 @@ if __name__ == '__main__':
     if sys.platform.startswith('darwin'):
       default_gyp_generators = 'ninja,xcode'
     elif sys.platform.startswith('win'):
-      default_gyp_generators = 'ninja,msvs'
+      default_gyp_generators = 'ninja,msvs-ninja'
     elif sys.platform.startswith('cygwin'):
-      default_gyp_generators = 'ninja,msvs'
+      default_gyp_generators = 'ninja,msvs-ninja'
     else:
       default_gyp_generators = 'ninja'
     os.environ[ENVVAR_GYP_GENERATORS] = default_gyp_generators