Remove 1em font-size from .plugin-menu-page code CSS style.

Fixes issue with monospaced code font overlapping text above and below it. See the `y` in "you" in the screenshot below; the bottom gets cut off:

![screen shot 2013-11-27 at 2 45 53 pm](https://f.cloud.github.com/assets/53005/1634570/d01e74be-579c-11e3-892c-4a34bc7aa061.png)

Removing the `1em` font size fixes the problem:

![screen shot 2013-11-27 at 2 46 22 pm](https://f.cloud.github.com/assets/53005/1634574/ee66a702-579c-11e3-88e3-e6740a64585f.png)