Fix previous added test by relaxing promise check.

The previous incantation check specifically for a .caught() method
on promises, but this is something specific to bluebird. While the
standard method is .catch(), we now rely on await to unpack any
exceptions so this check should be sufficient.

lib/evaluateSnippets.js

@@ -28,11 +28,7 @@ try {
 }
 
 function isPromise(value) {
-  return (
-    value &&
-    typeof value.then === 'function' &&
-    typeof value.caught === 'function'
-  );
+  return value && typeof value.then === 'function';
 }
 
 function getErrorMessage(expect, format, error) {
@@ -110,6 +106,7 @@ module.exports = async function(snippets, options) {
               ? snippet.code
               : `(function () {${transpile(snippet.code)}})();`
           );
+
           if (!isPromise(promise)) {
             throw new Error(
               `Async code block did not return a promise or throw\n${snippet.code}`