CookieAssertionTests expects language tag compliance by default

Issue: SPR-16700

spring-test/src/test/java/org/springframework/test/web/servlet/samples/standalone/resultmatchers/CookieAssertionTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2017 the original author or authors.
+ * Copyright 2002-2018 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -70,8 +70,8 @@ public class CookieAssertionTests {
 
 	@Test
 	public void testEqualTo() throws Exception {
-		this.mockMvc.perform(get("/")).andExpect(cookie().value(COOKIE_NAME, "en_US"));
-		this.mockMvc.perform(get("/")).andExpect(cookie().value(COOKIE_NAME, equalTo("en_US")));
+		this.mockMvc.perform(get("/")).andExpect(cookie().value(COOKIE_NAME, "en-US"));
+		this.mockMvc.perform(get("/")).andExpect(cookie().value(COOKIE_NAME, equalTo("en-US")));
 	}
 
 	@Test