Add some proguard rules

Author: izaak

app/proguard-rules.pro

@@ -18,4 +18,11 @@
 
 # If you keep the line number information, uncomment this to
 # hide the original source file name.
-#-renamesourcefileattribute SourceFile
+#-renamesourcefileattribute SourceFile
+
+-dontwarn javax.lang.model.element.Element*
+-dontwarn javax.lang.model.element.ElementKind*
+-dontwarn javax.lang.model.element.Modifier*
+-dontwarn javax.lang.model.type.TypeMirror*
+-dontwarn javax.lang.model.type.TypeVisitor*
+-dontwarn javax.lang.model.util.SimpleTypeVisitor8*