Move sqlite driver to v3

[mattes]

[haisum]

@maxvw created sqlite3 driver in 386ce00 and updated README.md to remove todo. Then @dhui updated README.md in 8684cad and marked sqlite3 as todo again. So what's the current state of sqlite3 driver? Are there any pending issues those are yet to be resolved?

[dhui]

The official repo is now at golang-migrate/migrate

sqlite should work in migrate but it's not officially supported since TravisCI builds were failing due to cgo issues. In other words, you'll need to build migrate yourself if you're using sqlite.

For more info, see: golang-migrate/migrate@15611d4

Feel free to open a PR to officially add sqlite support again!