chore(deps): pin 'google-crc32c < 0.2dev' (#160)

Prepare for upcoming version, which will namespace the module to avoid
conflict with the ICRAR version.

See: googleapis/python-crc32c#29

setup.py

@@ -25,7 +25,7 @@
 
 REQUIREMENTS = [
     'six',
-    'google-crc32c >= 0.1.0; python_version>="3.5"',
+    'google-crc32c >= 0.1.0, < 0.2dev; python_version>="3.5"',
     'crcmod >= 1.7; python_version=="2.7"',
 ]
 EXTRAS_REQUIRE = {