fixed Java 8 generics issue
LinkedSets to maintain order
enable Java 8 on Travis
Remove override annotation
Merge branch 'develop' into fix/java8-compability

* develop:
  fixed OGC logo URL in footer
  speed up build by fetching SCM revision only once
  Fix duplicate column definition.
  removed repository declaration in sub-pom
override XPathFactory implementation for SAXON

see https://saxonica.plan.io/issues/1944
Merge pull request #29 from autermann/fix/java8-compability

Oracle JDK 8 compatibility