since the git command output is redirected to the http response body, the golang
http server automatically adds a 200 status before sending the body. If the git
command fails we cannot return an http error anymore but must close the
connection to let the client know that the request failed.
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
