use placeholders when generating paths with missing params

Author: yyx990803

lib/route-recognizer.js

@@ -59,7 +59,7 @@ DynamicSegment.prototype = {
   },
 
   generate: function(params) {
-    return params[this.name];
+    return params[this.name] || ":" + this.name;
   }
 };
 
@@ -74,7 +74,7 @@ StarSegment.prototype = {
   },
 
   generate: function(params) {
-    return params[this.name];
+    return params[this.name] || ":" + this.name;
   }
 };