Avoid "Unsupported let compound assignment"

This Crankshift bailout reason prevents optimizing add() function.

lib/path-set.js

@@ -45,7 +45,7 @@ class PathSet {
     for (let i = 0; i < path.length; ++ i) {
       let fragment = path[i];
       if (fragment === "*")
-        wildcard |= 1 << i;
+        wildcard = wildcard | (1 << i);
 
       if (!this.fragmentIndex[i])
         this.fragmentIndex[i] = {};