Modify the `git-logg` alias to succinctly summarize.

This commit changes the format of the `git-logg` output like this:

```
969d252 [WIP] Modify the `git-logg` alias.                                     Kazuhiro MUSASHI     27 minutes ago
e7f4c4e Merge branch 'id/9'                                                    Kazuhiro MUSASHI     5 months ago
d180c0f Insert `=>` when toggling `=`.                                         Kazuhiro MUSASHI     5 months ago
```