Upgrade to Gradle Nexus Publish Plugin 2.0.0

Closes gh-21

build.gradle

@@ -7,7 +7,7 @@ buildscript {
         }
     }
     dependencies {
-        classpath "io.github.gradle-nexus:publish-plugin:1.3.0"
+        classpath "io.github.gradle-nexus:publish-plugin:2.0.0"
         classpath "org.graceframework:grace-gradle-plugin:$graceVersion"
         classpath "org.gradle:test-retry-gradle-plugin:1.4.0"
         classpath "io.spring.gradle:dependency-management-plugin:$springDependencyManagementPluginVersion"