On a git process error don't write the error message to the response body since
it'll break the git protocol and don't try to write the status header (since it's not
possible as it was automatically written by the go http server before writing
the body).
Just a raw replace of "github.com/pkg/errors".
Next steps will improve errors (like remote errors, api errors, not exist errors
etc...) to leverage its functionalities
Simone Gotti