Add missing comma from #1429 (#1433)

Turns out this is what was causing the OOM when building binaryen since
we were clobbering the EMSDK_NUM_CORES environment variable by mistake.

See #1429

Author: sbc100

emsdk.py

@@ -2632,7 +2632,7 @@ def construct_env_with_vars(env_vars_to_add):
   # of the SDK but we want to remove that from the current environment
   # if no such tool is active.
   # Ignore certain keys that are inputs to emsdk itself.
-  ignore_keys = set(['EMSDK_POWERSHELL', 'EMSDK_CSH', 'EMSDK_CMD', 'EMSDK_BASH', 'EMSDK_FISH'
+  ignore_keys = set(['EMSDK_POWERSHELL', 'EMSDK_CSH', 'EMSDK_CMD', 'EMSDK_BASH', 'EMSDK_FISH',
                      'EMSDK_NUM_CORES', 'EMSDK_NOTTY', 'EMSDK_KEEP_DOWNLOADS'])
   env_keys_to_add = set(pair[0] for pair in env_vars_to_add)
   for key in os.environ: