test: fixup parallel/test-async-wrap-post-did-throw.js

* change var to let
* replace equal with strictEqual

PR-URL: https://github.com/nodejs/node/pull/8625
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: James M Snell <jasnell@gmail.com>

test/parallel/test-async-wrap-post-did-throw.js

@@ -8,17 +8,17 @@ if (!common.hasCrypto) {
 
 const assert = require('assert');
 const async_wrap = process.binding('async_wrap');
-var asyncThrows = 0;
-var uncaughtExceptionCount = 0;
+let asyncThrows = 0;
+let uncaughtExceptionCount = 0;
 
 process.on('uncaughtException', (e) => {
-  assert.equal(e.message, 'oh noes!', 'error messages do not match');
+  assert.strictEqual(e.message, 'oh noes!', 'error messages do not match');
 });
 
 process.on('exit', () => {
   process.removeAllListeners('uncaughtException');
-  assert.equal(uncaughtExceptionCount, 1);
-  assert.equal(uncaughtExceptionCount, asyncThrows);
+  assert.strictEqual(uncaughtExceptionCount, 1);
+  assert.strictEqual(uncaughtExceptionCount, asyncThrows);
 });
 
 function init() { }