test: improvements in test fixtures symlinked

- using strictEqual instead equal
- common dependency should be the first one
- using path.join instead relative path

PR-URL: nodejs#10182
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Italo A. Casas <me@italoacasas.com>

test/fixtures/module-require-symlink/symlinked.js

@@ -1,13 +1,13 @@
 'use strict';
-const assert = require('assert');
 const common = require('../../common');
+const assert = require('assert');
+const foo = require('./foo');
 const path = require('path');
 
 const linkScriptTarget = path.join(common.fixturesDir,
-  '/module-require-symlink/symlinked.js');
+  'module-require-symlink', 'symlinked.js');
 
-var foo = require('./foo');
-assert.equal(foo.dep1.bar.version, 'CORRECT_VERSION');
-assert.equal(foo.dep2.bar.version, 'CORRECT_VERSION');
-assert.equal(__filename, linkScriptTarget);
+assert.strictEqual(foo.dep1.bar.version, 'CORRECT_VERSION');
+assert.strictEqual(foo.dep2.bar.version, 'CORRECT_VERSION');
+assert.strictEqual(__filename, linkScriptTarget);
 assert(__filename in require.cache);