Use integer as userId instead of String

src/Utils.js

@@ -1,3 +1,5 @@
+/* global crypto */
+
 /*
   EventHandler is an helper class for constructing custom types.
 
@@ -818,8 +820,10 @@ export default function Utils (Y) {
   }
   Y.utils.createSmallLookupBuffer = createSmallLookupBuffer
 
-  // Generates a unique id, for use as a user id.
-  // Thx to @jed for this script https://gist.github.com/jed/982883
-  function generateGuid(a){return a?(a^Math.random()*16>>a/4).toString(16):([1e7]+-1e3+-4e3+-8e3+-1e11).replace(/[018]/g,generateGuid)} // eslint-disable-line
-  Y.utils.generateGuid = generateGuid
+  function generateUserId () {
+    let arr = new Uint32Array(1)
+    crypto.getRandomValues(arr)
+    return arr[0]
+  }
+  Y.utils.generateUserId = generateUserId
 }