Fix :shadowJar task. Take 2.

This time, wait for the subprojects to be evaluated before trying
to get their shadowJar tasks (otherwise they won't be there).

build.gradle

@@ -51,13 +51,15 @@ subprojects {
     apply plugin: 'eclipse'
     apply plugin: 'idea'
 
-    def shadowJar = it.tasks.findByName('shadowJar')
+    afterEvaluate {
+        def shadowJar = project.tasks.findByName('shadowJar')
         if (shadowJar != null && shadowJar.hasProperty('archivePath') && project.name != 'core') {
             def rootTask = rootProject.tasks.shadowJar
             rootTask.dependsOn shadowJar
             rootTask.from shadowJar.archivePath
         }
     }
+}
 
 // Workaround specific to CI build to guarantee correct ordering of
 //   ./gradlew --parallel shadowJar :1.8:setCoreVersion