Ensure spring-test builds against HttpComponents 4.5

This is necessary to ensure that the version of HtmlUnit that we use is
compatible with HttpComponents 4.5.

Issue: SPR-13158

build.gradle

@@ -1032,6 +1032,7 @@ project("spring-test") {
 		}
 		testCompile("org.hsqldb:hsqldb:${hsqldbVersion}")
 		testCompile("org.slf4j:slf4j-jcl:${slf4jVersion}")
+		testCompile("org.apache.httpcomponents:httpclient:$httpclientVersion")
 	}
 
 	task testNG(type: Test) {