Patch QNameCache to use ConcurrentHashMap to avoid serialization

(cherry picked from commit aab89a6)

Align with new XPP dependency.

Version 2.1.2 has been skipped.

Branch 2.1.x is built for Java 1.8.

Use JDK 1.8 for build this.branch.

version 2.1.1

Change minimum Java version to 8 for branch 2.1.x

Fix CI with OpenJDK 7 - use HTTP instead of HTTPS for Gradle (dom4j#31)

Fix CI with OpenJDK 7 - use HTTP instead of HTTPS for Gradle