Fix golint errors under confidence 0.1

1 files changed, 10 insertions, 2 deletions

diff --git a/sheet.go b/sheet.go
index 011ecb8..b5c3e6c 100644
--- a/sheet.go
+++ b/sheet.go
@@ -1,3 +1,11 @@
+// Package excelize providing a set of functions that allow you to write to
+// and read from XLSX files. Support reads and writes XLSX file generated by
+// Microsoft Excel™ 2007 and later. Support save file without losing original
+// charts of XLSX. This library needs Go version 1.8 or later.
+//
+// Copyright 2016 - 2018 The excelize Authors. All rights reserved. Use of
+// this source code is governed by a BSD-style license that can be found in
+// the LICENSE file.
 package excelize
 
 import (
@@ -371,7 +379,7 @@ func (f *File) SetSheetBackground(sheet, picture string) error {
 	}
 	ext, ok := supportImageTypes[path.Ext(picture)]
 	if !ok {
-		return errors.New("Unsupported image extension")
+		return errors.New("unsupported image extension")
 	}
 	pictureID := f.countMedia() + 1
 	rID := f.addSheetRelationships(sheet, SourceRelationshipImage, "../media/image"+strconv.Itoa(pictureID)+ext, "")
@@ -441,7 +449,7 @@ func (f *File) deleteSheetFromContentTypes(target string) {
 //
 func (f *File) CopySheet(from, to int) error {
 	if from < 1 || to < 1 || from == to || f.GetSheetName(from) == "" || f.GetSheetName(to) == "" {
-		return errors.New("Invalid worksheet index")
+		return errors.New("invalid worksheet index")
 	}
 	f.copySheet(from, to)
 	return nil