Bump version to 3.0.2-SNAPSHOT for next development cycle

This should have been done right after we cut the 3.0.1 release
(i.e., development for 3.0.2 started with SHA:
25cd2a35963b27f9569660d17de7948122d44f2f).
Merge pull request #524 from dotta/3.0.x/bump-version

3.0.x/bump version