Use evm on TravisCI

- [Emacsのバージョンマネージャ "evm" がEmacs LispのCIにおすすめ - Copy/Cut/Paste/Hatena](http://k1low.hatenablog.com/entry/2014/04/15/203856)
- [Library s not found after installed by cask? · Issue #172 · cask/cask](https://github.com/cask/cask/issues/172#issuecomment-32716449)
Should be installed emacs before cask install
No run test on Emacs23

```
cask upgrade-cask: error: Emacs 24 required, yours is Emacs 23.4.1.
```
Merge pull request #5 from gongo/use_evm_on_ci

Use evm on TravisCI
Use undercover.el