Fix uncaught type error on clicking lexical this

[ryu39]

Thank you for nice documents about ES6 features.

I found a slight issue on clicking 'Lexical this' in side menu, please see the following image.

When 'Lexical this' link is clicked, the ev.target does not contain <a> tag element, but <code> tag element under <a> tag. And <code> tag does not have href attribute, so error is occurred.

I fixed this issue by using $(this) instead of $(ev.target). Also the argument ev is not used, so I removed it.