Improved: Raise build error if Javadoc is not valid.

This is part of the Javadoc refactoring issue as discussed in (OFBIZ-9144)


git-svn-id: https://svn.apache.org/repos/asf/ofbiz/trunk@1774933 13f79535-47bb-0310-9956-ffa450edef68
diff --git a/build.gradle b/build.gradle
index 57e6853..3640b7a 100644
--- a/build.gradle
+++ b/build.gradle
@@ -35,7 +35,7 @@
 // java settings
 def jvmArguments = ['-Xms128M', '-Xmx1024M']
 ext.ofbizMainClass = 'org.apache.ofbiz.base.start.Start'
-javadoc.failOnError = false
+javadoc.failOnError = true
 sourceCompatibility = '1.8'
 targetCompatibility = '1.8'