evil-forward-word-begin gets stuck on interpolated strings in elixir-mode

Originally reported by: **Aaron Jensen (Bitbucket: [aaronjensen1](https://bitbucket.org/aaronjensen1), GitHub: Unknown)**

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I don't know if this is somehow an elixir-mode bug, but it seems like it probably isn't? Let me know if it would be better to open it there. Thanks!

## Repro ##

* `make emacs`
* Install elixir-mode, make sure it is in load-path
* `(require 'elixir-mode)`
* `M-x elixir-mode`
* Insert: `"test #{test} test"`
* Go to beg of line w/ `0`, hit `w` several times.

### Expected ###

Go through the test words, passing each one

### Actual ###

Get stuck on the `#`, no amount of `w` goes past it

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- Bitbucket: https://bitbucket.org/lyro/evil/issue/693