Update documentation

- `TermApp::LocoMenu#process`
- `TermApp::ReadBoardMenu#process_key`
- `TermApp::ReadBoardMenu#scroll`
Simplify logic processing `selected_menu`
Update gems
Regenerate offenses of RuboCop
Align chaining methods
Use inline `if` statement for single-line body
fix misplaced codes
Merge pull request #92 from yous/patch-cleanup

Cleanup
Redraw only highlighted lines when not scrolling

Introduce `@past_index` and redraw when it's nil. Redraw only
highlighted lines when `@past_index` and `@cur_index` is different.