test: favor strict equality check

Change use of `!=` in assertion to `assert.notStrictEqual()` check.

PR-URL: https://github.com/nodejs/node/pull/8130
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

test/pummel/test-tls-connect-memleak.js

@@ -27,7 +27,7 @@ tls.createServer({
 
   const options = { rejectUnauthorized: false };
   tls.connect(common.PORT, '127.0.0.1', options, function() {
-    assert(junk.length != 0);  // keep reference alive
+    assert.notStrictEqual(junk.length, 0);  // keep reference alive
     setTimeout(done, 10);
     global.gc();
   });