Fix content type parsing error for HttpCore 4.4.6+

[mikejhill]

Targeting this fork for the same reason as #5.

A bugfix in Apache HttpCore 4.4.6 (HTTPCORE-423, f8f55e88) causes UrlRewriteFilter PUT/POST requests to fail if their content type includes a charset (e.g., Content-Type: application/json; charset=UTF-8). This is because the ContentType.create(String) method used to use its parameter directly as the MIME type (incorrect behavior -- included charset in MIME type), but now tries to read it as a MIME type. The alternative factory method ContentType.parse(String) parses the full string for both MIME type and charset.

We didn't notice this issue until recently since we don't pull transitive dependencies for UrlRewriteFilter. A separate library update upgraded us from HttpCore v4.4.5 to v4.4.13, which fixed the ContentType.create(String) method but broke UrlRewriteFilter.