The following changed Java compatibility to 1.7:
In 5.1.4, java.util.Objects was introduced by an unused import statement into ActionQueue by HHH-9864. This seemed to only affect only some versions of Java 1.6.
In 5.1.11, java.util.regex.Pattern.UNICODE_CHARACTER_CLASS was introduced into ReflectHelper by HHH-11377.
The following changed Java compatibility to 1.8:
In 5.1.17, the upgrade to dom4j to 2.2.1 by HHH-12964.
The README and migration notes should reflect these changes.