fix: fix broken stats test

One test broke due to c4934ca [1].

If promises are used, you needn't pass `done` as parameter of
the callback in.

[1]: c4934ca#diff-0a6449ecfa8b9e3d807f53dde24eca71R66

Author: vmx

js/src/stats.js

@@ -63,7 +63,7 @@ module.exports = (common) => {
       })
     })
 
-    it('.bw Promise', function (done) {
+    it('.bw Promise', function () {
       if (!withGo) {
         console.log('Not supported in js-ipfs yet')
         this.skip()