[v1.02] added special handling for updating 'content-type' header

applies patch made to "moz-rewrite":
    https://github.com/warren-bank/moz-rewrite
in commit:
    https://github.com/warren-bank/moz-rewrite/commit/7ea64debc9883d355aeca311da603ca5ef0ee996

noticed while testing the following rule in the response data set:

[
{
    "url": "\\.(json|jsonp)$",
    "headers": {
        "content-type" : "application/json"
    }
},
{
    "url": "[\\?&]callback=",
    "headers": {
        "content-type" : "application/json"
    }
}
]

..that an Exception was being logged.

* turns out that the API treats this header differently
* rather than calling the normal `setResponseHeader` method,
  a special read/write attribute `contentType` needs to be changed

now, the above rule works beautifully.