Duplicated snippet in ruby.snippets

after this commit of @babybeasimple : https://github.com/babybeasimple/vim-snippets/commit/e3e7ab1b45dc264c7aa5348a677371f3d83e80ab#L0R1036

```bash
408| snippet sel
409|     select { |${1:e}| ${2} }
```

and

```bash
1037| snippet sel
1038|     it { should ensure_length_of :${1} }
```

Renamed the latter to `itsel`. In fact, I would rename all specs snippets to
`it%xxx%`, so they don't block other names.