Fix go build vcs errors

[amacneil]

Fix CI errors related to go embedding vcs info in binaries. It seems reasonable to include this info.

Error was:

$ docker-compose run --rm --no-deps dev make build ls
rm -rf dist
go build -o dist/dbmate -tags netgo,osusergo,sqlite_omit_load_extension,sqlite_json  -ldflags '-s -extldflags "-static"' .
error obtaining VCS status: exit status 128
	Use -buildvcs=false to disable VCS stamping.
make: *** [Makefile:34: build] Error 1

And underlying error was:

$ docker-compose run --rm --no-deps dev git status
fatal: detected dubious ownership in repository at '/src'
To add an exception for this directory, call:

	git config --global --add safe.directory /src

Solution:

• Don't exclude .git directory from docker so it's available in the docker build
• Mark /src as safe for git in dockerfile

Closes #384