Adds .innerWidth as an option to calculate elm width

fixed an issue with IE10 and 11 not properly recalculating window width on resize.

before:
the width of elm would update on resize
![screen shot 2014-05-15 at 1 16 23 pm](https://cloud.githubusercontent.com/assets/877072/2988082/8ec5c808-dc55-11e3-9f6a-ea72717157cb.png)

after:
![screen shot 2014-05-15 at 1 16 43 pm](https://cloud.githubusercontent.com/assets/877072/2988091/a18c0db2-dc55-11e3-9a1b-f7d26bc154d3.png)