Perform compatibility testing against REST Assured 4.0 and 4.1

Closes gh-640

spring-restdocs-restassured/build.gradle

@@ -13,4 +13,11 @@ dependencies {
 
 test {
 	jvmArgs "-javaagent:${configurations.jacoco.asPath}=destfile=${buildDir}/jacoco.exec,includes=org.springframework.restdocs.*"
+}
+
+matrixTest {
+	restAssured {
+		group = 'io.rest-assured'
+		versions = ['4.0.0', '4.1.1']
+	}
 }