Fix proper response for BucketExists API (#1038)

when resp 404 Not Found, BucketExists error should be nil, exists==false

Fixes #1036

api-stat.go

@@ -47,6 +47,10 @@ func (c Client) BucketExists(bucketName string) (bool, error) {
 		return false, err
 	}
 	if resp != nil {
+		resperr := httpRespToErrorResponse(resp, bucketName, "")
+		if ToErrorResponse(resperr).Code == "NoSuchBucket" {
+			return false, nil
+		}
 		if resp.StatusCode != http.StatusOK {
 			return false, httpRespToErrorResponse(resp, bucketName, "")
 		}

appveyor.yml

@@ -16,7 +16,7 @@ install:
   - set PATH=%GOPATH%\bin;c:\go\bin;%PATH%
   - go version
   - go env
-  - go get -u github.com/golang/lint/golint
+  - go get -u golang.org/x/lint/golint
   - go get -u github.com/remyoudompheng/go-misc/deadcode
   - go get -u github.com/gordonklaus/ineffassign
   - go get -u golang.org/x/crypto/argon2