Provide more context in lint error message

Author: wincent

resources/lint/no-async.js

@@ -16,7 +16,10 @@ module.exports = function(context) {
         if (node.async) {
           context.report(
             node,
-            'async functions are not allowed outside of the test suite'
+            'async functions are not allowed outside of the test suite ' +
+            'because older versions of NodeJS do not support them ' +
+            'without additional runtime dependencies. Instead, use explicit ' +
+            'Promises.'
           );
         }
       },