Add gitignore for Ruby
Update vim-plug

- junegunn/vim-plug@cb08d6036b7be9ed6e7fe87cf4c128944f17923a
- junegunn/vim-plug@0e907d4f387faa8b5ff8d50de945e38b48783782
- junegunn/vim-plug@f31477407a584c47e4b95390a538e0f2d5630e7c