Prevent git commands from launching an interactive editor

Since git switched its rebase backend from apply to merge, it launches
a commit message editor on `git rebase --continue`. This causes
rebase-helper to hang indefinitely.
Prevent that from happening by explicitly reconfiguring the editor in
the git repo.

Signed-off-by: Nikola Forró <nforro@redhat.com>

rebasehelper/patcher.py

@@ -323,6 +323,8 @@ def init_git(cls, directory):
         repo.git.config('rebasehelper.state', state, local=True)
         repo.git.config('user.name', GitHelper.get_user(), local=True)
         repo.git.config('user.email', GitHelper.get_email(), local=True)
+        # prevent git commands from launching an interactive editor
+        repo.git.config('core.editor', 'true', local=True)
         repo.git.add(all=True)
         repo.index.commit('Initial commit', skip_hooks=True)
         return repo, state