Fix executing npm under cygwin.

script/bootstrap.py

@@ -11,7 +11,7 @@ from lib.util import execute, scoped_cwd
 SOURCE_ROOT = os.path.abspath(os.path.dirname(os.path.dirname(__file__)))
 VENDOR_DIR = os.path.join(SOURCE_ROOT, 'vendor')
 PYTHON_26_URL = 'https://chromium.googlesource.com/chromium/deps/python_26'
-NPM = 'npm.cmd' if sys.platform == 'win32' else 'npm'
+NPM = 'npm.cmd' if sys.platform in ['win32', 'cygwin'] else 'npm'
 
 
 def main():