content/static/html/helpers: open source files in separate tab

Change-Id: I949bf5825a4d351785398c41426adaee76945ef2
Reviewed-on: https://go-review.googlesource.com/c/pkgsite/+/259937
Trust: Julie Qiu <julie@golang.org>
Run-TryBot: Julie Qiu <julie@golang.org>
TryBot-Result: kokoro <noreply+kokoro@google.com>
Reviewed-by: Jamal Carvalho <jamal@golang.org>
diff --git a/content/static/html/helpers/_unit_files.tmpl b/content/static/html/helpers/_unit_files.tmpl
index 1c34322..282e46e 100644
--- a/content/static/html/helpers/_unit_files.tmpl
+++ b/content/static/html/helpers/_unit_files.tmpl
@@ -12,7 +12,7 @@
     <div>
       <ul class="UnitFiles-fileList">
         {{- range .SourceFiles -}}
-          <li class="UnitFiles-file"><a href="{{.URL}}" title="{{.Name}}">{{.Name}}</a></li>
+          <li class="UnitFiles-file"><a href="{{.URL}}" target="_blank" title="{{.Name}}">{{.Name}}</a></li>
         {{- end -}}
       </ul>
     </div>