_content/doc/go1.18: go fix requires go.mod go 1.18 for go:build change

Fixes golang/go#51873

Change-Id: Ied51c36a30cd18ff4a84d164e62df2690931d94f
Reviewed-on: https://go-review.googlesource.com/c/website/+/396879
Run-TryBot: Ian Lance Taylor <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>
Reviewed-by: Bryan Mills <[email protected]>
Trust: Ian Lance Taylor <[email protected]>

Author: ianlancetaylor

_content/doc/go1.18.html

@@ -473,7 +473,7 @@ <h4 id="go-build-lines"><code>//go:build</code> lines</h4>
 all supported versions of Go now understand <code>//go:build</code> lines.
 In Go 1.18, <code>go</code> <code>fix</code> now removes the now-obsolete
 <code>//</code> <code>+build</code> lines in modules declaring
-<code>go</code> <code>1.17</code> or later in their <code>go.mod</code> files.
+<code>go</code> <code>1.18</code> or later in their <code>go.mod</code> files.
 </p>
 
 <p>