Runtime error w/ Ruby 1.8.7 & Addressable >= 2.4.0
Runtime error w/ Ruby 1.8.7 & Addressable >= 2.4.0

  Addressable >= 2.4.0 not longer supports Ruby 1.8.7.
  However we don't want to restrict the Addressable version for all Ruby versions.
  This change raises a Runtime error if the user tries to use Ruby <= 1.8.7 with
  Addressable >= 2.4.0.
bblimke/webmock,davidbegin/webmock,taiki45/webmock