fix glock failing to 'get' inside githooks
fix glock failing to 'get' inside githooks

When glock is run in a git hook and tries to `go get` a new dependency,
the `git clone` operation fails with a message like this:

    fatal: working tree '.' already exists.

This is because the git hook is executed with GIT_WORK_TREE and GIT_DIR
env vars set, which interfere with git operations on other repos.
Using `env` to execute glock with these specifically unset should avoid the issue.

veteranlu/cockroach,maxlang/cockroach,arjun4084346/cockroach,glycerine/cockroach,paperstreet/cockroach,petermattis/cockroach,nieyy/cockroach,bg451/cockroach,nieyy/cockroach,petermattis/cockroach,vivekmenezes/cockroach,maxlang/cockroach,veteranlu/cockroach,cuongdo/cockroach,bg451/cockroach,veteranlu/cockroach,nieyy/cockroach,petermattis/cockroach,il9ue/cockroach,cockroachdb/cockroach,vaibhavarora/cockroach,vivekmenezes/cockroach,arjun4084346/cockroach,nieyy/cockroach,bg451/cockroach,nieyy/cockroach,il9ue/cockroach,arjun4084346/cockroach,paperstreet/cockroach,sunya123/cockroach,cockroachdb/cockroach,maxlang/cockroach,arjun4084346/cockroach,vaibhavarora/cockroach,vivekmenezes/cockroach,petermattis/cockroach,veteranlu/cockroach,cuongdo/cockroach,maxlang/cockroach,sunya123/cockroach,glycerine/cockroach,cuongdo/cockroach,il9ue/cockroach,vaibhavarora/cockroach,cuongdo/cockroach,sunya123/cockroach,arjun4084346/cockroach,cockroachdb/cockroach,sunya123/cockroach,vaibhavarora/cockroach,bg451/cockroach,il9ue/cockroach,il9ue/cockroach,paperstreet/cockroach,glycerine/cockroach,sunya123/cockroach,petermattis/cockroach,sunya123/cockroach,arjun4084346/cockroach,paperstreet/cockroach,bg451/cockroach,arjun4084346/cockroach,maxlang/cockroach,maxlang/cockroach,paperstreet/cockroach,cockroachdb/cockroach,cockroachdb/cockroach,glycerine/cockroach,maxlang/cockroach,paperstreet/cockroach,nieyy/cockroach,arjun4084346/cockroach,veteranlu/cockroach,vivekmenezes/cockroach,vivekmenezes/cockroach,cuongdo/cockroach,vivekmenezes/cockroach,vaibhavarora/cockroach,veteranlu/cockroach,paperstreet/cockroach,sunya123/cockroach,veteranlu/cockroach,vaibhavarora/cockroach,cuongdo/cockroach,veteranlu/cockroach,cockroachdb/cockroach,glycerine/cockroach,il9ue/cockroach,vaibhavarora/cockroach,cockroachdb/cockroach,glycerine/cockroach,nieyy/cockroach,sunya123/cockroach,petermattis/cockroach,vivekmenezes/cockroach,il9ue/cockroach,paperstreet/cockroach,glycerine/cockroach,il9ue/cockroach,cuongdo/cockroach,bg451/cockroach,cuongdo/cockroach,petermattis/cockroach,bg451/cockroach,vivekmenezes/cockroach,glycerine/cockroach,nieyy/cockroach,maxlang/cockroach,cockroachdb/cockroach,vaibhavarora/cockroach,petermattis/cockroach