Sort input file list

so that _ubjson.so builds in a reproducible way
in spite of indeterministic filesystem readdir order
and http://bugs.python.org/issue30461

See https://reproducible-builds.org/ for why this is good.

This PR was done while working on reproducible builds for openSUSE.

setup.py

@@ -89,7 +89,7 @@ def build_extension(self, ext):
     license='Apache License 2.0',
     packages=['ubjson'],
     zip_safe=False,
-    ext_modules=([Extension('_ubjson', glob('src/*.c'), extra_compile_args=COMPILE_ARGS)]
+    ext_modules=([Extension('_ubjson', sorted(glob('src/*.c')), extra_compile_args=COMPILE_ARGS)]
                  if BUILD_EXTENSIONS else []),
     cmdclass={"build_ext": BuildExtWarnOnFail},
     keywords=['ubjson', 'ubj'],