Release v0.3.0

Summary: Bump the version to v0.3.0.

Test Plan: Run `make && blubber --version` and verify the output.

Reviewers: thcipriani, hashar, demon, #release-engineering-team

Reviewed By: thcipriani, #release-engineering-team

Tags: #release-engineering-team

Differential Revision: https://phabricator.wikimedia.org/D1014

VERSION

-0.2.0
+0.3.0