build: Add gradle build system and upgrade to use jndn version 0.9

Change-Id: I5e8c355dd3ad1e87d2ac06ec78dcf8fa66b9bc08
diff --git a/.travis.yml b/.travis.yml
index dff5f3a..4ddd19c 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -1 +1,4 @@
 language: java
+jdk:
+  - oraclejdk7
+