Expand and update REST Assured compatibility testing

Closes gh-688

Author: wilkinsona

spring-restdocs-restassured/build.gradle

@@ -18,6 +18,6 @@ test {
 matrixTest {
 	restAssured {
 		group = 'io.rest-assured'
-		versions = ['4.0.0', '4.1.1']
+		versions = ['4.0.0', '4.1.2', '4.2.0', '4.3.1']
 	}
 }