_content: fix download table overflow

Fixes golang/go#59949.

Change-Id: Ia0c633f935334ade7292d7b35e18315fa77e04b9
Reviewed-on: https://go-review.googlesource.com/c/website/+/498055
Run-TryBot: Jamal Carvalho <jamal@golang.org>
Reviewed-by: Hyang-Ah Hana Kim <hyangah@gmail.com>
Auto-Submit: Jamal Carvalho <jamal@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>

Author: jamalc

_content/dl.tmpl

@@ -99,6 +99,7 @@ go install golang.org/dl/{{.Version}}@latest
 {{end}}
 
 {{define "download-files"}}
+<div style="overflow:auto;">
 <table class="downloadtable">
 <thead>
 <tr class="first">
@@ -121,6 +122,7 @@ go install golang.org/dl/{{.Version}}@latest
   {{range .Files}}{{template "download-file" .}}{{end}}
 {{end}}
 </table>
+</div>
 {{end}}
 
 {{define "download-file"}}