Fix some tests

There is one behaviour change (you have to POST an array to a function
endpoint if you are sending a body), and also a message converter that
needed to be removed so that arrays are not toStringed in the response
body.

spring-cloud-function-samples/spring-cloud-function-sample-compiler/src/test/java/com/example/SampleApplicationTests.java

@@ -41,8 +41,8 @@ public class SampleApplicationTests {
 	@Test
 	public void lowercase() {
 		assertThat(new TestRestTemplate().postForObject(
-				"http://localhost:" + port + "/test", "it works",
-				String.class)).isEqualTo("it works!!!");
+				"http://localhost:" + port + "/test", "[\"it works\"]",
+				String.class)).isEqualTo("[\"it works!!!\"]");
 	}
 
 }