encrypt_secret: remove the trailing '/' when building url

Change-Id: Ie534063b85d333abfcc4116b4e3903299941f139
diff --git a/tools/encrypt_secret.py b/tools/encrypt_secret.py
index 2a4ea1d..c0ee9be 100755
--- a/tools/encrypt_secret.py
+++ b/tools/encrypt_secret.py
@@ -58,7 +58,7 @@
                         "to standard output.")
     args = parser.parse_args()
 
-    req = Request("%s/%s.pub" % (args.url, args.project))
+    req = Request("%s/%s.pub" % (args.url.rstrip('/'), args.project))
     pubkey = urlopen(req)
 
     if args.infile: