test: add regex to assert.throws

Make sure test matches this specific error message.

PR-URL: nodejs#11815
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Yuta Hiroto <hello@about-hiroppy.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

test/parallel/test-vm-run-in-new-context.js

@@ -38,7 +38,7 @@ assert.strictEqual('passed', result);
 console.error('thrown error');
 assert.throws(function() {
   vm.runInNewContext('throw new Error(\'test\');');
-});
+}, /^Error: test$/);
 
 global.hello = 5;
 vm.runInNewContext('hello = 2');