doc: note that x509 cert parsing rejects some more certs now

Fixes #23711

Author: bradfitz

doc/go1.10.html

@@ -785,7 +785,8 @@ <h3 id="minor_library_changes">Minor changes to the library</h3>
 <a href="/pkg/crypto/x509/#Certificate"><code>Certificate</code></a> fields
 <code>URIs</code>, <code>PermittedIPRanges</code>, <code>ExcludedIPRanges</code>,
 <code>PermittedEmailAddresses</code>, <code>ExcludedEmailAddresses</code>,
-<code>PermittedURIDomains</code>, and <code>ExcludedURIDomains</code>.
+<code>PermittedURIDomains</code>, and <code>ExcludedURIDomains</code>. Certificates with
+invalid values for those fields are now rejected.
 </p>
 
 <p>