Task publishMavenPublication should be declared an explicit dependency on Sign

Closes gh-842

Author: rainboyan

build.gradle

@@ -233,6 +233,11 @@ subprojects { project ->
             onlyIf { isReleaseVersion }
         }
 
+        TaskCollection<Sign> signingTasks = tasks.withType(Sign)
+        tasks.withType(PublishToMavenRepository).configureEach {
+            mustRunAfter(signingTasks)
+        }
+
         javadoc {
             if (JavaVersion.current().isJava9Compatible()) {
                 options.addBooleanOption('html5', true)