remove scala 2.9 support

Signed-off-by: Tsuyoshi Ozawa <ozawa.tsuyoshi@gmail.com>
Add @xerial as a developer

Signed-off-by: Tsuyoshi Ozawa <ozawa.tsuyoshi@gmail.com>
Updated publish URI to use HTTPS

Signed-off-by: Tsuyoshi Ozawa <ozawa.tsuyoshi@gmail.com>
Update Installation section

Signed-off-by: Tsuyoshi Ozawa <ozawa.tsuyoshi@gmail.com>