Bug fix in signature V4 method and update test case

[iMac0de]

No description provided.

[RockfordWei]

I checked out your branch but the testing reported on testSign() but succeded on testSample():

XCTAssertEqual failed: ("a59369a9c5c0cb3b5fc34e5ef689de2bc6cfb6e1ee2ada35c6def5bb35a1da9f") is not equal to ("6b555ea915ec8a5ee592ccfeec21a4d8d0ee27cfb29c8349fd80118f462ec23b") - 

May I ask why? A bit confused.

[iMac0de]

In fact, the new V4 signature take in account the bucket name. AWS S3 accept only unique bucket name, so I couldn't create a bucket named fishpool and make the test with another bucket name. I think this why the assert equal is failing.

However, it allows me to fix a little issue on the test.