[pom] Update nexus-staging-maven-plugin to 1.6.8
[pom] Update nexus-staging-maven-plugin to 1.6.8

hazendaz/formatter-maven-plugin,revelc/formatter-maven-plugin,ctubbsii/formatter-maven-plugin,hazendaz/formatter-maven-plugin,ctubbsii/formatter-maven-plugin,hazendaz/formatter-maven-plugin,revelc/formatter-maven-plugin,ctubbsii/formatter-maven-plugin,revelc/formatter-maven-plugin,hazendaz/formatter-maven-plugin,ctubbsii/formatter-maven-plugin,revelc/formatter-maven-plugin