Merge pull request hustcc#54 from juliofeng/patch-1

Update 4.shellSort.md

Author: shouao

4.shellSort.md

@@ -69,7 +69,7 @@ def shellSort(arr):
 func shellSort(arr []int) []int {
 	length := len(arr)
 	gap := 1
-	for gap < gap/3 {
+	for gap < length/3 {
 		gap = gap*3 + 1
 	}
 	for gap > 0 {