Revert to Alpine 3.6 for the Bitbucket image
Revert to Alpine 3.6 for the Bitbucket image

Git 2.15 exhibits issues with Bitbucket Server 5.6.0. Even though Git
2.15 support has (??) been added to Bitbucket Server 5.6.0
(https://jira.atlassian.com/browse/BSERV-10310), Git 2.15 is not yet
listed on the Supported platforms page
(https://confluence.atlassian.com/bitbucketserver/supported-platforms-77
6640981.html).

ianharrier/docker-bitbucket