Spring auto-reconfiguration changes to web_xml_modifier

These changes track Ben Hale's changes to the Java buildpack, incorporating the latest revisions to auto-reconfiguration: https://github.com/cloudfoundry/java-buildpack/blob/d3d17c550b721dd3c4bcbf33b8d9ed0f2f01e8e5/lib/java_buildpack/framework/spring_auto_reconfiguration/web_xml_modifier.rb