[xhr] getResponseHeader should work case-insensitive (#21)

Currently, the spec does not state anything about case-sensitivity with respect to response header names. In the W3C version of the spec (http://www.w3.org/TR/XMLHttpRequest/#the-getresponseheader()-method) it is stated that a header is a case-insensitive match for a response header.

To me it makes more sense to ignore the case in matching response headers.

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Reply to this email directly or view it on GitHub:
https://github.com/whatwg/xhr/issues/21