Fix bug with isStandardBrowserEnv (#597)

[eu81273]

document.createElement is not function in Internet Explorer 8.
But isStandardBrowserEnv checks standard browser environment like below.

function isStandardBrowserEnv() {
  return (
    typeof window !== 'undefined' &&
    typeof document !== 'undefined' &&
    typeof document.createElement !== 'function'
  );
}

As I mentioned above, document.createElement is not function(is object) in Internet Explorer 8, so isStandardBrowserEnv determine wrong; and XDomainRequest is not working in IE8.

[coveralls]

Changes Unknown when pulling a87e0b7 on eu81273:master into ** on mzabriskie:master**.

[nickuraltsev]

Closing in favor of #731.