test: refactor test-buffer-bytelength

* assert.equal -> assert.strictEqual.

PR-URL: nodejs#9808
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Prince John Wesley <princejohnwesley@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>

test/parallel/test-buffer-bytelength.js

@@ -27,7 +27,7 @@ assert.strictEqual(Buffer.byteLength(ascii), 3);
 
 // ArrayBuffer
 var buffer = new ArrayBuffer(8);
-assert.equal(Buffer.byteLength(buffer), 8);
+assert.strictEqual(Buffer.byteLength(buffer), 8);
 
 // TypedArray
 var int8 = new Int8Array(8);