Simple fix for error in IE when parsing AWS response

[sbiastoch]

IE is buggy when using innerHTML to access a node element's content, resulting in undefined. Furthermore children does not work consistently as well, again returning undefined. This two IE bugs cause uploads to fail when using AWS S3 Upload as the response from AWS cannot be parsed correctly.

The workaround replaces all affected occurrences of

1. children[0] by firstChild.firstChild
2. innerHTML by textContent (which is also more appropriate as we do not want to parse HTML and is thereby faster)
   Those two functions are very well supported across all browsers as firstChild is part of the ancient DOM-Level 1 specification and textContent is supported since IE9.

This fixes #325 and probably makes PR #462 and #332 unnecessary.

[vrajroham]

Thanks for your contribution. Will review and merge this soon.