Update Firefox/Chrome screenshots and Chrome version (#8515)

tests/screenshots

@@ -1 +1 @@
-Subproject commit 80b5030c7b7e395d7a421dcd238df670f02b41a7
+Subproject commit ce9907a1e9f05abceeb9be656b4d1d8d58f0d5bf

uitest/src/test/java/com/vaadin/tests/VerifyBrowserVersionTest.java

@@ -40,7 +40,7 @@ public class VerifyBrowserVersionTest extends MultiBrowserTest {
             // Chrome version does not necessarily match the desired version
             // because of auto updates...
             browserIdentifier = getExpectedUserAgentString(
-                    getDesiredCapabilities()) + "55";
+                    getDesiredCapabilities()) + "56";
         } else {
             browserIdentifier = getExpectedUserAgentString(desiredCapabilities)
                     + desiredCapabilities.getVersion();