nfd: Update to version 0.3.1

Fixes: #4
diff --git a/nfd/Makefile b/nfd/Makefile
index 1844a8e..c3e0d2c 100644
--- a/nfd/Makefile
+++ b/nfd/Makefile
@@ -2,13 +2,13 @@
 GIT_URL=https://github.com/named-data/NFD.git
 
 # Tag name or commit hash for checkout
-GIT_VERSION=NFD-0.3.0
+GIT_VERSION=NFD-0.3.1
 
 # Package name
 NAME=nfd
 
 # Package version
-VERSION=0.3.0
+VERSION=0.3.1
 
 # PPA version
 PPA_VERSION=2