* Serve .patch for pull requests

Closes #3259
Updates "git" module, for GetFormatPatch

* Handle io.Copy error

- Update import paths from github.com/go-gitea to code.gitea.io
- Fix import path for travis

See https://docs.travis-ci.com/user/languages/go#Go-Import-Path

* Replace gogits/git-module dependency with go-gitea/git

Fixes #92

* Remove git alias for git module import (not needed)