doc/contribute: avoid using the word "change list".
doc/contribute: avoid using the word "change list".

Neither the Gerrit UI nor its docs use the term CL or changelist.

Change-Id: Ic19fddc660ec4f008f10fd207e4ac6349431ff5d
Reviewed-on: https://go-review.googlesource.com/48595
Reviewed-by: Brad Fitzpatrick <ae9783c0b0efc69cd85ab025ddd17aa44cdc4aa5@golang.org>

josharian/go,nawawi/go,Cofyc/go,CAFxX/go,josharian/go,CAFxX/go,nawawi/go,josharian/go,polyverse-security/go,josharian/go,golang/go,Cofyc/go,Cofyc/go,akutz/go,polyverse-security/go,golang/go,polyverse-security/go,vsekhar/elastic-go,CAFxX/go,nawawi/go,polyverse-security/go,golang/go,vsekhar/elastic-go,josharian/go,josharian/go,golang/go,nawawi/go,cloudflare/go,Cofyc/go,nawawi/go,josharian/go,cloudflare/go,CAFxX/go,polyverse-security/go,akutz/go,vsekhar/elastic-go,Cofyc/go,codestation/go,vsekhar/elastic-go,vsekhar/elastic-go,codestation/go,vsekhar/elastic-go,codestation/go,codestation/go,akutz/go,akutz/go,golang/go,codestation/go,vsekhar/elastic-go,akutz/go,christopher-henderson/Go,golang/go,golang/go,Cofyc/go,CAFxX/go,josharian/go,codestation/go,cloudflare/go,Cofyc/go,cloudflare/go,cloudflare/go,golang/go,CAFxX/go,akutz/go,polyverse-security/go,Cofyc/go,CAFxX/go,nawawi/go,nawawi/go,akutz/go,polyverse-security/go,vsekhar/elastic-go,cloudflare/go,cloudflare/go,polyverse-security/go,akutz/go,nawawi/go,codestation/go,cloudflare/go,codestation/go,CAFxX/go