Don't quote numeric values as strings when building google analytics commands.

This fixes an error Google's Tag Assistant Chrome Extension points out on all our sites when setting _setSiteSpeedSampleRate
Better checking of numeric values when quoting.

This prevents strings that are also numbers from being used as a number in the analytics commands. Thanks to @gauthierm for pointing it out.
Merge pull request #99 from isaacgrant/dont-quote-me-bro

Don't quote numeric values as strings when building google analytics commands.