Bumped version of publishing plugin

We need to use newer version of Gradle Plugin Portal publishing plugin. Otherwise Shipkit won't be able to publish to Gradle Plugin Portal. The error message from Travis CI:

This version of the com.gradle.plugin-publish plugin is no longer supported due to a critical security vulnerability. Please update to the latest version of the com.gradle.plugin-publish plugin (...)

Author: mockitoguy

subprojects/shipkit/shipkit.gradle

@@ -22,7 +22,7 @@ dependencies {
 
     compile "com.github.cliftonlabs:json-simple:2.1.2"
     compile 'com.jfrog.bintray.gradle:gradle-bintray-plugin:1.8.4'
-    compile "com.gradle.publish:plugin-publish-plugin:0.9.10"
+    compile "com.gradle.publish:plugin-publish-plugin:0.12.0"
     compile 'com.googlecode.java-diff-utils:diffutils:1.3.0'
 
     testCompile("org.spockframework:spock-core:1.3-groovy-2.4") {