test: assert.throws() should include a RegExp

PR-URL: https://github.com/nodejs/node/pull/997://github.com/nodejs/node/pull/9976
Reviewed-By: Prince John Wesley <princejohnwesley@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>

test/parallel/test-child-process-detached.js

@@ -18,7 +18,7 @@ process.on('exit', function() {
   assert(persistentPid !== -1);
   assert.throws(function() {
     process.kill(child.pid);
-  });
+  }, /^Error: kill ESRCH$/);
   assert.doesNotThrow(function() {
     process.kill(persistentPid);
   });