Exit fatally if submodule is not present

Author: asottile

setup.py

@@ -29,6 +29,7 @@
           'try the following command', file=sys.stderr)
     print('  git submodule update --init', file=sys.stderr)
     print(file=sys.stderr)
+    exit(1)
 
 sources = ['pysass.cpp']
 headers = []