use fmt.Errorf instead of error.New() (#149)

fission/function.go

@@ -17,7 +17,6 @@ limitations under the License.
 package main
 
 import (
-	"errors"
 	"fmt"
 	"io/ioutil"
 	"net/http"
@@ -45,9 +44,7 @@ func fnFetchCode(filePath string) []byte {
 
 		defer resp.Body.Close()
 		if resp.StatusCode != http.StatusOK {
-
+			err = fmt.Errorf("%v - HTTP response returned non 200 status", resp.StatusCode)
-			err = errors.New(fmt.Sprintf("%v - HTTP response returned non 200 status",
-				resp.StatusCode))
 			checkErr(err, fmt.Sprintf("download function"))
 		}