Drop Commons Net back to 2.0

Change-Id: I45b362a7a8290ab34cc44ec638e35697d33a635c
Signed-off-by: Shawn O. Pearce <sop@google.com>
diff --git a/pom.xml b/pom.xml
index 1ddea33..6123b50 100644
--- a/pom.xml
+++ b/pom.xml
@@ -532,7 +532,7 @@
       <dependency>
         <groupId>commons-net</groupId>
         <artifactId>commons-net</artifactId>
-        <version>2.1</version>
+        <version>2.0</version>
       </dependency>
 
       <dependency>