ndn-tools: Fixing package (downgrade sphinx requirement)

Change-Id: I948b59eda16c55285b26031e9e699ab4c8c9a83b
diff --git a/ndn-tools/debian/patches/series b/ndn-tools/debian/patches/series
index e69de29..661c3d7 100644
--- a/ndn-tools/debian/patches/series
+++ b/ndn-tools/debian/patches/series
@@ -0,0 +1 @@
+downgrade-sphinx.patch