Update com.gradle.plugin-publish to v0.12.0

Apparently, there was a security vulnerability in the version of the
plugin we were using and publishing to the plugin portal with it
doesn't work anymore:

    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 found here:
         https://plugins.gradle.org/plugin/com.gradle.plugin-publish
      You can read more about this vulnerability here:
         https://blog.gradle.org/plugin-portal-update

build.gradle

@@ -1,7 +1,7 @@
 plugins {
     id 'groovy'
     id 'maven-publish'
-    id 'com.gradle.plugin-publish' version '0.10.1'
+    id 'com.gradle.plugin-publish' version '0.12.0'
     id 'com.github.johnrengelman.shadow' version '5.1.0'
     id "com.github.sherter.google-java-format" version '0.8'
 }