mark commons-lang3 as optional since TypeUtils is used only as a fallback mechanism, albeit a useful one

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/proxy/branches/version-2.0-work@979750 13f79535-47bb-0310-9956-ffa450edef68
diff --git a/stub/pom.xml b/stub/pom.xml
index 61ef4cb..97aa52f 100644
--- a/stub/pom.xml
+++ b/stub/pom.xml
@@ -34,6 +34,7 @@
             <groupId>org.apache.commons</groupId>
             <artifactId>commons-lang3</artifactId>
             <version>3.0-SNAPSHOT</version>
+            <optional>true</optional>
         </dependency>
         <dependency>
             <groupId>junit</groupId>