Use of Number.isInteger limits browser support

[jeff-phillips-18]

The Number.isInteger() method is not supported in Internet Explorer 11 and earlier versions. Looks like the use was added in version 1.18.11

[spadgett]

MDN has this as a polyfill

  return typeof value === 'number' && 
    isFinite(value) && 
    Math.floor(value) === value;

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Number/isInteger#Polyfill

[rodneyrehm]

This was introduced in #345 and I'm sorry to say that the last couple of months doing ES6-only has made me completely oblivious to this - sorry.

@jeff-phillips-18 @spadgett does either one of you want to send a PR for this?

[jeff-phillips-18]

@rodneyrehm I will send a PR shortly

[maiamcc]

(...for anyone who cares (probably very few folks), also experiencing this problem on phantomjs 2.1.1.)