Add missing devDependdency

Author: dignifiedquire

package.json

@@ -36,7 +36,8 @@
     "pull-through": "^1.0.18",
     "tap": "^5.7.2",
     "tape": "^4.4.0",
-    "testling": "^1.7.1"
+    "testling": "^1.7.1",
+    "wsurl": "^1.0.0"
   },
   "browser": {
     "ws": false,