Upgraded Brakeman gem

Went from 2.6.2 to 2.6.3. Better to upgrade and stay current with all
the security scanning than to lag behind.
Merge pull request #481 from ministryofjustice/breakeman2.6.3

Upgraded Brakeman gem
Merge branch 'master' into postcode_lookup_2

* master:
  Upgraded Brakeman gem