Use compatibility with Java 1.8

Change-Id: I06f8381f475fe3b995a224d782cfd706b83e7142
diff --git a/build.gradle b/build.gradle
index e8f5ca4..58c7625 100644
--- a/build.gradle
+++ b/build.gradle
@@ -12,8 +12,8 @@
 group = 'net.named-data.jndn-extra'
 version = '1.0.2-SNAPSHOT'
 
-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 {