Install vim-snippets and enable it.

see:

- [Shougo/neosnippet.vim](https://github.com/Shougo/neosnippet.vim)
- [honza/vim-snippets](https://github.com/honza/vim-snippets)

This commit fixes #260.
Merge branch 'id/260'
Update NeoSnippet configuration.

see:

- [Shougo/neosnippet.vim](https://github.com/Shougo/neosnippet.vim)

This commit fixes #258.
Merge branch 'id/258'
Use serverspec.snip when opening *_rspec.rb.

This commit fixes #259.
Merge branch 'id/259'