doc: document Go 1.9.4 and Go 1.8.7

Change-Id: I50928e7747f43858fc863b53cfb5b63e208d6932
Reviewed-on: https://team-review.git.corp.google.com/213447
Reviewed-by: Andrew Bonventre <[email protected]>

Author: rsc

doc/devel/release.html

@@ -57,6 +57,12 @@ <h3 id="go1.9.minor">Minor revisions</h3>
 1.9.3 milestone</a> on our issue tracker for details.
 </p>
 
+<p>
+go1.9.4 (released 2018/02/07) includes a security fix to “go get”.
+See the <a href="https://github.com/golang/go/issues?q=milestone%3AGo1.9.4">Go
+1.9.4</a> milestone on our issue tracker for details.
+</p>
+
 <h2 id="go1.8">go1.8 (released 2017/02/16)</h2>
 
 <p>
@@ -114,6 +120,13 @@ <h3 id="go1.8.minor">Minor revisions</h3>
 1.8.6 milestone</a> on our issue tracker for details.
 </p>
 
+<p>
+go1.8.7 (released 2018/02/07) includes a security fix to “go get”.
+It contains the same fix as Go 1.9.4 and was released at the same time.
+See the <a href="https://github.com/golang/go/issues?q=milestone%3AGo1.8.7">Go
+1.8.7</a> milestone on our issue tracker for details.
+</p>
+
 <h2 id="go1.7">go1.7 (released 2016/08/15)</h2>
 
 <p>