fix issue #1366 (Javadoc not built for jme3-examples)

jme3-examples/gradle.properties

@@ -1,5 +1,5 @@
-# When running this project we don't need javadoc to be built.
-buildJavaDoc = false
-
 # We want assertions, because this is the test project.
 assertions = true
+
+# Build javadoc per Github issue #1366
+buildJavaDoc = true