fix InvalidAccessKeyId error according to amazon documentation (#4404)

http://docs.aws.amazon.com/AmazonS3/latest/API/ErrorResponses.html

cmd/api-errors.go

@@ -230,7 +230,7 @@ var errorCodeResponse = map[APIErrorCode]APIError{
 		HTTPStatusCode: http.StatusInternalServerError,
 	},
 	ErrInvalidAccessKeyID: {
-		Code:           "InvalidAccessKeyID",
+		Code:           "InvalidAccessKeyId",
 		Description:    "The access key ID you provided does not exist in our records.",
 		HTTPStatusCode: http.StatusForbidden,
 	},

cmd/bucket-handlers_test.go

@@ -68,7 +68,7 @@ func testGetBucketLocationHandler(obj ObjectLayer, instanceType, bucketName stri
 			locationResponse:   []byte(""),
 			errorResponse: APIErrorResponse{
 				Resource: "/" + bucketName + "/",
-				Code:     "InvalidAccessKeyID",
+				Code:     "InvalidAccessKeyId",
 				Message:  "The access key ID you provided does not exist in our records.",
 			},
 			shouldPass: false,