Add regex to exclude tag combiners and guardian weekly subs pages.

Attempt to exclude tag combiners like ``/books/books+tone/reviews`` and subscription trailblock pages like ``/weekly/subscribe/about-guardian-weekly``

CC @guardian/contentapi @guardian/content-platforms
Yeah you have a point @philwills  I have tested this now with positive and negative cases in the Ruby REPL at Nic's suggestion:

`irb> "/books/books+tone/reviews" =~ %r{\+}
=> 12`

`irb> "/books/bookstone/reviews" =~ %r{\+}
=> nil`

So I'll check that version in and merge.