bump version and changelog for v2.10.0-rc1

CHANGELOG.md

 # Changelog
 All notable changes to Ergo will be documented in this file.
 
-## [2.10.0-rc1] - 2022-05-15
+## [2.10.0-rc1] - 2022-05-16
 
 We're pleased to be publishing the release candidate for 2.10.0 (the official release should follow in a week or so).
 

irc/version.go

 
 const (
 	// SemVer is the semantic version of Ergo.
-	SemVer = "2.10.0-unreleased"
+	SemVer = "2.10.0-rc1"
 )
 
 var (