Upgrade to junit 4.13.1

Change-Id: Ic2d2077b592cc7df28427c7ae78c981ad15d2bc2
diff --git a/build.gradle b/build.gradle
index dc1803f..fa80ca3 100644
--- a/build.gradle
+++ b/build.gradle
@@ -22,7 +22,7 @@
 dependencies {
   api 'net.named-data:jndn:0.24'
 
-  testImplementation 'junit:junit:4.12'
+  testImplementation 'junit:junit:4.13.1'
   testRuntimeOnly 'org.slf4j:slf4j-api:1.7.30'
 }