Fix IE11

[joefiorini]

Fixes #6

[dbrans]

@aokolish @joefiorini
global isFinite and Number.isFinite are slightly different.

Would you mind writing a function numberIsFinite that uses Number.isFinite if it's there and otherwise uses the global isFinite but special-cases anyString => false and null => false?

[joefiorini]

@dbrans how about we just use the polyfill suggested on that page? https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Number/isFinite#Polyfill

[dbrans]

@joefiorini perfect. Do you or @aokolish want to update this PR?

[joefiorini]

@dbrans i'll get to it tomorrow

[joefiorini]

@dbrans turns out lodash includes this polyfill, so I went ahead and used that instead (using a package that includes just that function for now).