Ensure git is installed in alpine image

[klmitch]

Apparently, a recent update to the upstream alpine image has resulted in git no longer being installed by default in the alpine container image. This pull request ensures that git is installed.

Closes issue #346

[tianon]

Duplicate of #345 (most recently), but see also #250 (comment); #119, #140, #153, #157, #166, #198, #209, #230, #239, #241, #251, #328.

[klmitch]

Duplicate of #345 (most recently), but see also #250 (comment); #119, #140, #153, #157, #166, #198, #209, #230, #239, #241, #251, #328.

Yeah, that's a coworker addressing the same issue as me; I didn't notice that he had said he was opening a PR :)

[tianon]

Whew, that makes so much more sense -- the synchronized timing was giving me anxiety thinking something bigger was afoot. 😄

I'll close this then in favor of the discussion over there. 👍