internal/goversion: update Version to 1.18

This is the start of the Go 1.18 development cycle, so update the
Version value accordingly. It represents the Go 1.x version that
will soon open up for development (and eventually become released).

Updates #40705
Updates #47351

Change-Id: Icfb99e28529a3c9fb7394e114a34586f613dfcbf
Reviewed-on: https://go-review.googlesource.com/c/go/+/341590
Trust: Carlos Amedee <[email protected]>
Run-TryBot: Carlos Amedee <[email protected]>
TryBot-Result: Go Bot <[email protected]>
Reviewed-by: Dmitri Shuralyov <[email protected]>
Reviewed-by: Matthew Dempsky <[email protected]>
Reviewed-by: Alexander Rakoczy <[email protected]>

Author: cagedmantis

src/internal/goversion/goversion.go

@@ -9,4 +9,4 @@ package goversion
 //
 // It should be updated at the start of each development cycle to be
 // the version of the next Go 1.x release. See golang.org/issue/40705.
-const Version = 17
+const Version = 18