Upgrade to junit 4.13.1

Change-Id: I8ac932670273bcf343e675191329486cc68ff19e
diff --git a/build.gradle b/build.gradle
index 31e8b4e..54a5a7b 100644
--- a/build.gradle
+++ b/build.gradle
@@ -43,7 +43,7 @@
 dependencies {
   api 'net.named-data:jndn:0.24'
 
-  testImplementation 'junit:junit:4.12'
+  testImplementation 'junit:junit:4.13.1'
   testImplementation 'net.named-data.jndn-extra:jndn-mock:1.2.0'
   testRuntimeOnly 'org.slf4j:slf4j-api:1.7.30'
 }