Change variable names of Google Analytics tracking code

`i` `s` `o` `g` `r` `a` `m` -> `L` `I` `C` `e` `N` `C` `E`

It is generated by [isogram](https://github.com/shinnn/isogram), a google analytics code generator used by [gulp website](https://github.com/gulpjs/gulpjs.github.io/blob/fc2a237ef4b476dd9428fce0da77c6bd3f8b925d/index.html#L134).

I can update this PR if you prefer other variable names, such as:
* `g` `i` `t` `h` `u` `b`
* `c` `h` `o` `O` `s` `e`