Corrected regression test for dynamic routing
Corrected regression test for dynamic routing

no issue

- The reason for the test failure was:
- Bump in express version: https://github.com/TryGhost/Ghost/commit/5a316c3c804c3823d0df55359c6e32d8c7333c1f)
- Which included bump of it's internal dependency `send` to version send@0.17.1: https://github.com/expressjs/express/releases/tag/4.17.0)
- Which had a change in how 'xml' type was interpreted: https://github.com/pillarjs/send/pull/154/files
- Because in Ghost documentation for dynamic routing, we clearly state to use `contetn_type: text/xml` instead of just `content_type:xml` the test was considered to be not up to date (ref. https://docs.ghost.org/api/handlebars-themes/routing/routes/)
- Returning `content-type: text/xml; charset=UTF-8` stays in line with the rest of Ghost codebase
- WARNING: when using `res.type('xml')` for whatever reason in the codebase be awere that express will send `application/xml` header which is not the convention used throughout the codebase

janvt/Ghost,kevinansfield/Ghost,bitjson/Ghost,Kikobeats/Ghost,JohnONolan/Ghost,kevinansfield/Ghost,ErisDS/Ghost,TryGhost/Ghost,kevinansfield/Ghost,JohnONolan/Ghost,e10/Ghost,janvt/Ghost,Kikobeats/Ghost,TryGhost/Ghost,bitjson/Ghost,JohnONolan/Ghost,e10/Ghost,ErisDS/Ghost,ErisDS/Ghost,TryGhost/Ghost,Kikobeats/Ghost