Fix JUnit jar version in build.gradle

tlatools/build.gradle

@@ -15,7 +15,7 @@ repositories {
 
 dependencies {
 	implementation(files('lib/javax.mail.jar'))
-	testImplementation(files('lib/easymock-3.3.1.jar', 'lib/jpf.jar', 'lib/junit-4.8.2.jar', 'lib/javax.mail.jar'))
+	testImplementation(files('lib/easymock-3.3.1.jar', 'lib/jpf.jar', 'lib/junit-4.12.jar', 'lib/javax.mail.jar'))
 }
 
 sourceSets {