Bugfix: Output stacktrace to support typescript errors.

Before this patch the errorhandling would fail with the error: "ERROR: null". Debug showed that the error "caught error sometime before command handler: TypeError: Cannot convert object to primitive value"

lib/cli/run.js

@@ -369,7 +369,7 @@ exports.handler = async function (argv) {
   try {
     await runMocha(mocha, argv);
   } catch (err) {
-    console.error('\n' + (err.stack || `Error: ${err.message || err}`));
+    console.error('\n' + (err.stack || `Error: ${err && err.message}`), err);
     process.exit(1);
   }
 };