test: refactor using template string

Use template string where it's appropriate.

PR-URL: #17314
Reviewed-By: Daijiro Wachi <daijiro.wachi@gmail.com>
Reviewed-By: Vse Mozhet Byt <vsemozhetbyt@gmail.com>
Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Luigi Pinca <luigipinca@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>

Author: kt3k

test/abort/test-zlib-invalid-internals-usage.js

@@ -13,8 +13,8 @@ if (process.argv[2] === 'child') {
   assert.strictEqual(child.stdout.toString(), '');
   assert.ok(child.stderr.includes(
     'WARNING: You are likely using a version of node-tar or npm that ' +
-    'is incompatible with this version of Node.js.' + os.EOL +
+    `is incompatible with this version of Node.js.${os.EOL}` +
     'Please use either the version of npm that is bundled with Node.js, or ' +
     'a version of npm (> 5.5.1 or < 5.4.0) or node-tar (> 4.0.1) that is ' +
-    'compatible with Node.js 9 and above.' + os.EOL));
+    `compatible with Node.js 9 and above.${os.EOL}`));
 }