Add SSLHost logic to ModifyResponseHeaders()

[dtomcej]

This PR:

• Updates the ModifyResponseHeaders method to modify the scheme of the location header if the following conditions are true:
  • The Request is a TLS request
  • There is an SSLHost defined
  • The Response contains the SSLHost with an http scheme
  • The Response does not contain a port
• Adds tests to verify that the behaviour is consistent.

Fixes #61

[unrolled]

Looks good to me! Thanks @dtomcej for the PR, and thanks @keesverruijt for reviewing!! I'll tag this merge as v1.0.5.