strings: remove empty line

Change-Id: Ibdca4f7002585b00d7f69d710285a8e0f69c598a
GitHub-Last-Rev: eb8f800c986c8ac4a81705158ecc730c35e1c5c2
GitHub-Pull-Request: golang/go#28659
Reviewed-on: https://go-review.googlesource.com/c/148477Reviewed-by: Russ Cox <rsc@golang.org>

src/strings/strings.go

@@ -1040,5 +1040,4 @@ func indexRabinKarp(s, substr string) int {
 		}
 	}
 	return -1
-
 }