Use Java 8

Change-Id: I0d31b1facf2d026cf07d834712064fb902bbfe9e
diff --git a/build.gradle b/build.gradle
index ec94957..0a5c50d 100644
--- a/build.gradle
+++ b/build.gradle
@@ -18,8 +18,8 @@
 group = 'net.named-data.jndn-extra'
 version = '1.1.1'
 
-sourceCompatibility = JavaVersion.VERSION_1_7
-targetCompatibility = JavaVersion.VERSION_1_7
+sourceCompatibility = JavaVersion.VERSION_1_8
+targetCompatibility = JavaVersion.VERSION_1_8
 compileJava.options.encoding = 'UTF-8'
 
 repositories {