Add php-semver-checker-git to travis after_script.

php-semver-checker-git will provide a suggested semantic version for the current set of changes since the last tag.

Author: tomzx

.travis.yml

@@ -16,3 +16,5 @@ script:
 after_script:
     - wget https://scrutinizer-ci.com/ocular.phar
     - php ocular.phar code-coverage:upload --format=php-clover log/coverage.xml
+    - wget https://tomzx.github.io/php-semver-checker-git/php-semver-checker-git.phar
+    - php php-semver-checker-git.phar suggest src src --allow-detached -vvv