Update commons-net dependency

The name was changed from commons_net to commons-net in gerrit
core change I1e75690fe.

Change-Id: Ife1fa0bb066f7c319b40db5ef79ce1cd56922e23

BUILD

diff --git a/BUILD b/BUILD
index e77b68b..f66c844 100644
--- a/BUILD
+++ b/BUILD
@@ -11,6 +11,6 @@
         "Implementation-URL: https://gerrit.googlesource.com/plugins/motd",
     ],
     deps = [
-        "@commons_net//jar:neverlink",
+        "@commons-net//jar:neverlink",
     ],
 )