modified SIGINT handling #3570 (#3602)

* Updated SIGINT handler based on comment from #3570

Signed-off-by: jayasankar <jayasankar.m@gmail.com>

lib/cli/run-helpers.js

@@ -196,14 +196,15 @@ exports.singleRun = (mocha, {files = [], exit = false} = {}) => {
   mocha.files = files;
   const runner = mocha.run(exit ? exitMocha : exitMochaLater);
 
-  process.on('SIGINT', () => {
+  process.once('SIGINT', () => {
     debug('aborting runner');
     runner.abort();
 
     // This is a hack:
     // Instead of `process.exit(130)`, set runner.failures to 130 (exit code for SIGINT)
     // The amount of failures will be emitted as error code later
     runner.failures = 130;
+    setImmediate(() => process.kill(process.pid, 'SIGINT'));
   });
 };