removed instructions re: headless browser testing. updated minimum  PHP requirements to 5.4
removed headless/phantomjs browser profiles from behat config.
removed phantomjs from composer config.
recreated composer lock file.
removed phantomjs from travis build script.
updated Link module to version 7.x-1.3
Merge pull request #65 from stopfstedt/update_link_module

Updated Link module to version 7.x-1.3.
Merge pull request #67 from stopfstedt/remove_phantom_js

Remove phantom.js/headless test runner configuration.