Rewrite `Math.pow` ⇒ `**`

JavaScript pattern

ES7 introduced the exponentiation operator ** so that using Math.pow is no longer necessary.

Transforms Math.pow to exponentiation operator

BEFORE
var a = Math.pow(0, 1);
var b = Math.pow(0, b - 1);
var c = Math.pow(b + 1, b - 1);
var d = Math.pow(b + 1, 1);
AFTER
var a = (0) ** (1);
var b = (0) ** (b - 1);
var c = (b + 1) ** (b - 1);
var d = (b + 1) ** (1);