Bump tf-mot to 0.2.0.

PiperOrigin-RevId: 286096621

Author: alanchiao

tensorflow_model_optimization/python/core/version.py

@@ -16,8 +16,8 @@
 
 # We follow Semantic Versioning (https://semver.org/)
 _MAJOR_VERSION = '0'
-_MINOR_VERSION = '1'
-_PATCH_VERSION = '3'
+_MINOR_VERSION = '2'
+_PATCH_VERSION = '0'
 
 # When building releases, we can update this value on the release branch to
 # reflect the current release candidate ('rc0', 'rc1') or, finally, the official