Bump version number to v1.9.1 (and copyright year to 2021)

Author: benhoyt

goawk.go

@@ -43,8 +43,8 @@ import (
 )
 
 const (
-	version    = "v1.9.0"
-	copyright  = "GoAWK " + version + " - Copyright (c) 2019 Ben Hoyt"
+	version    = "v1.9.1"
+	copyright  = "GoAWK " + version + " - Copyright (c) 2021 Ben Hoyt"
 	shortUsage = "usage: goawk [-F fs] [-v var=value] [-f progfile | 'prog'] [file ...]"
 	longUsage  = `Standard AWK arguments:
   -F separator