Update docs copyright year

Author: jvalkeal

spring-shell-docs/src/main/asciidoc/index.adoc

@@ -8,7 +8,7 @@ Eric Bottard; Janne Valkealahti; Jay Bryant; Corneil du Plessis
 
 *{project-version}*
 
-(C) 2017 - 2022 VMware, Inc.
+(C) 2017 - 2023 VMware, Inc.
 
 _Copies of this document may be made for your own use and for distribution to
 others, provided that you do not charge any fee for such copies and further