Update python dependencies

Change-Id: Ic1ba3152160e9255d14ae66881e452a99930b0d8
diff --git a/ndns/debian/control b/ndns/debian/control
index 2d2dde6..095c779 100644
--- a/ndns/debian/control
+++ b/ndns/debian/control
@@ -2,9 +2,11 @@
 Priority: extra
 Maintainer: Alexander Afanasyev <alexander.afanasyev@ucla.edu>
 Build-Depends: debhelper (>= 9.20160709),
- python (>= 2.7.0),
+ python3 (>= 3.6.0),
  pkg-config (>= 0.26),
- libndn-cxx-dev (>= 0.8.0)
+ libndn-cxx-dev (>= 0.8.0),
+ python3-sphinx (>= 1.6.0),
+ git
 Standards-Version: 4.5.0
 Section: net
 Homepage: http://github.com/named-data/ndns