fix(build.py): git submodule update fails when installing by sdist

Author: Xmader

build.py

@@ -52,7 +52,7 @@ def copy_artifacts():
         execute("cp ./_spidermonkey_install/lib/libmozjs* ./python/pythonmonkey/", cwd=TOP_DIR)
 
 def build():
-    execute("git submodule update --init --recursive", cwd=TOP_DIR)
+    execute("git submodule update --init --recursive || echo 'Skipping. We are installing from an sdist tarball.'", cwd=TOP_DIR)
     ensure_spidermonkey()
     run_cmake_build()
     copy_artifacts()