Update vimrc

I found that you are using tpope's unimpared and `[e` and `]e` are from it, seeing .gitmodule. the rhs wasn't easy to read/maintain, so use more declarative names.

https://github.com/tpope/vim-unimpaired/blob/master/plugin/unimpaired.vim#L179

TODO: ditto in `[egv` and `]egv`
Merge pull request #1 from ujihisa/patch-1

Update vimrc