Fix issues with npm install of google-closure-compiler installing all dev packages as well. (#793)

emsdk.py

diff --git a/emsdk.py b/emsdk.py
index 48ac2a9..96a47e3 100644
--- a/emsdk.py
+++ b/emsdk.py
@@ -1411,7 +1411,7 @@
     print('Running post-install step: npm install', closure_compiler_native)
     try:
       subprocess.check_output(
-        [npm, 'install', closure_compiler_native],
+        [npm, 'install', '--production', '--no-optional', closure_compiler_native],
         cwd=directory, stderr=subprocess.STDOUT, env=env,
         universal_newlines=True)
     except subprocess.CalledProcessError as e: