fix the perf tests of OpenCV.js so that it can run on Node.js successfully

modules/js/perf/base.js

@@ -1,5 +1,10 @@
 if (typeof window === 'undefined') {
   var cv = require("../opencv");
+  if (cv instanceof Promise) {
+    loadOpenCV();
+  } else {
+    cv.onRuntimeInitialized = perf;
+  }
 }
 
 let gCvSize;
@@ -24,6 +29,10 @@ function getCvSize() {
   return gCvSize;
 }
 
+async function loadOpenCV() {
+  cv = await cv;
+}
+
 if (typeof window === 'undefined') {
   exports.getCvSize = getCvSize;
 }