Update Google Analytics script

`i,s,o,g,r,a,m` → `g,i,t,h,u,b`

It is generated by using [isogram](https://github.com/shinnn/isogram), inspired by [HTML5boilerplate](https://github.com/h5bp/html5-boilerplate/commit/48d49e96d6db282eb9686d31ebbc5cbbbdd4d966), and [well tested](https://travis-ci.org/shinnn/isogram).