Enable deprecation warnings

Change-Id: Ibb0fb80a14121809791c5137cd5eb9638de15d72
diff --git a/build.gradle b/build.gradle
index 4d059fe..9761d95 100644
--- a/build.gradle
+++ b/build.gradle
@@ -54,6 +54,10 @@
   from sourceSets.main.allSource
 }
 
+tasks.withType(JavaCompile) {
+  options.deprecation = true
+}
+
 tasks.withType(Test) {
   reports.html.destination = file("${reporting.baseDir}/${name}")
   testLogging {