glide {get,install,update} breaks vendor submodule #697

In our vendor workflow, we opted to make vendor a submodule, so we'd get the benefits of checking in deps (e.g. maintaining distribution, reproducibility, etc) without adding the actual content of dep changes to our main repo history (our vendor is ~200mb right now).

However, glide replaces the vendor directory with a newly built one after every operation, which has the side effect of deleting the vendor/.git submodule pointer.

Our current workaround is to just move .git aside and replace it after.