.gitignore: .egg-info => *.egg-info

Without this, I was getting this:

```
$ git status
On branch add_env_context_and_config_to_migration_context
Untracked files:
  (use "git add <file>..." to include in what will be committed)

	alembic.egg-info/

nothing added to commit but untracked files present (use "git add" to track)
```