Rename variables of Google Analytics script

`i` `s` `o` `g` `r` `a` `m` -> `E` `s` `n` `e` `x` `t`

It is generated by [isogram](https://github.com/shinnn/isogram), a GA script generator used by [gulp website](https://github.com/gulpjs/gulpjs.github.io/blob/fc2a237ef4b476dd9428fce0da77c6bd3f8b925d/index.html#L134).