Upgrade to commons-lang3 3.9

New features:
o LANG-1442: Javadoc pointing to Commons RNG.
o            Adding the Functions class.
o LANG-1411: Add isEmpty method to ObjectUtils Thanks to Alexander Tsvetkov.
o LANG-1422: Add null-safe StringUtils.valueOf(char[]) to delegate to String.valueOf(char[])
o LANG-1427: Add API org.apache.commons.lang3.SystemUtils.isJavaVersionAtMost(JavaVersion)


Changes:
o LANG-1416: Add more SystemUtils.IS_JAVA_XX variants.
o LANG-1416: Update to JUnit 5
o LANG-1417: Add @FunctionalInterface to ThreadPredicate and ThreadGroupPredicate
o LANG-1415: Update Java Language requirement to 1.8
o LANG-1436: Consolidate the StringUtils equals and equalsIgnoreCase Javadoc and implementation
o            (doc) Fix javadoc for 'startIndex' parameter of StringUtils.join() methods. GitHub PR #412. Thanks to Andrei Troie aft90.