test: fix isNAN->Number.isNAN

PR-URL: #17309
Reviewed-By: Yosuke Furukawa <yosuke.furukawa@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Daijiro Wachi <daijiro.wachi@gmail.com>
Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>
Reviewed-By: Jon Moss <me@jonathanmoss.me>
Reviewed-By: James M Snell <jasnell@gmail.com>

test/parallel/test-writedouble.js

@@ -189,8 +189,8 @@ function test(clazz) {
   // Darwin ia32 does the other kind of NaN.
   // Compiler bug.  No one really cares.
   assert(0x7F === buffer[15] || 0xFF === buffer[15]);
-  assert.ok(isNaN(buffer.readDoubleBE(0)));
-  assert.ok(isNaN(buffer.readDoubleLE(8)));
+  assert.ok(Number.isNaN(buffer.readDoubleBE(0)));
+  assert.ok(Number.isNaN(buffer.readDoubleLE(8)));
 }