Use lexical this outside tag scope

[MartinMuzatko]

https://github.com/voorhoede/riotjs-style-guide#assign-this-to-tag

With es6 lexical this syntax () => {} or function() {}.bind(this) it should be very easy to avoid something as redundant as var that = this or const tag = this

[jbmoelker]

Agree both are possible. Using const tag = this is simply our preference over function() {}.bind(this).

Also based on Angular Style Guide > var vm = this;.