debian: bump Standards-Version to the current one.

Fixes ancient-standards-version lintian warning.

debian/control

diff --git a/debian/control b/debian/control
index acf710a..da9c683 100644
--- a/debian/control
+++ b/debian/control
@@ -11,7 +11,7 @@
                libxslt1-dev,
                lsb-release,
                zlib1g-dev
-Standards-Version: 3.9.1
+Standards-Version: 3.9.8.0
 Homepage: http://nginx.org
 
 Package: nginx