Is there an existing issue for this?

• I have searched the existing issues

Current Behavior

Currently GIT_SSH_COMMAND has hardcoded ssh path in https://github.com/npm/git/blob/v4.0.4/lib/opts.js#L5

But there is also GIT_SSH env. var honored by standard git. The GIT_SSH_COMMAND should use GIT_SSH (and quoted) instead of ssh when GIT_SSH is non-empty.

Will fix npm/cli#2891 as I can confirm npm/cli#2891 (comment) fixes the problem.

Expected Behavior

GIT_SSH other than ssh/empty is honored.