Fix test for newer Jenkins versions (#227)

Dashboard string is not always included in the root page of the
Jenkins controller, nor should the test require that it is included.
It is enough to check that the page contains the well-known URL of the
Jenkins website.

Author: MarkEWaite

src/test/java/io/jenkins/plugins/httpclient/RobustHTTPClientIntegrationTest.java

@@ -67,7 +67,8 @@ public void createRobustHTTPClient() throws Exception {
     @Test
     public void testDownloadFile() throws Exception {
         client.downloadFile(f, j.getURL(), TaskListener.NULL);
-        assertThat(Files.readString(f.toPath()), containsString("<title>Dashboard [Jenkins]</title>"));
+        // Jenkins controller root page should always contain at lease one reference to Jenkins web site
+        assertThat(Files.readString(f.toPath()), containsString("https://www.jenkins.io/"));
     }
 
     /**