test: remove extraneous space

Change `require ('zlib');` to `require('zlib');` in conformance with
style in the rest of the code base. This is in preparation for enabling
linting for that issue.

PR-URL: https://github.com/nodejs/node/pull/8097
Reviewed-By: targos - Michaël Zasso <mic.besace@gmail.com>
Reviewed-By: jasnell - James M Snell <jasnell@gmail.com>
Reviewed-By: Roman Reiss <me@silverwind.io>

test/parallel/test-zlib-truncated.js

@@ -3,7 +3,7 @@
 
 require('../common');
 const assert = require('assert');
-const zlib = require ('zlib');
+const zlib = require('zlib');
 
 const inputString = 'ΩΩLorem ipsum dolor sit amet, consectetur adipiscing eli' +
                     't. Morbi faucibus, purus at gravida dictum, libero arcu ' +