all: upgrade to JUnit 4.12

diff --git a/documentation/server-reflection-tutorial.md b/documentation/server-reflection-tutorial.md
index 4cd68b6..025d3b0 100644
--- a/documentation/server-reflection-tutorial.md
+++ b/documentation/server-reflection-tutorial.md
@@ -28,7 +28,7 @@
 +  compile "io.grpc:grpc-services:${grpcVersion}"
    compile "io.grpc:grpc-stub:${grpcVersion}"
  
-   testCompile "junit:junit:4.11"
+   testCompile "junit:junit:4.12"
 --- a/examples/src/main/java/io/grpc/examples/helloworld/HelloWorldServer.java
 +++ b/examples/src/main/java/io/grpc/examples/helloworld/HelloWorldServer.java
 @@ -33,6 +33,7 @@ package io.grpc.examples.helloworld;