Verify that window size increases after maximize

For #169

t/01-driver.t

@@ -176,6 +176,9 @@ WINDOW: {
     is ($ret->{'width'}, 480, 'Got the right width');
     $ret = $driver->maximize_window();
     is ($ret, 1, "Got confirmation from maximize");
+    $ret = $driver->get_window_size();
+    ok ($ret->{'height'} > 640, 'Height has increased');
+    ok ($ret->{'width'} > 480, 'Width has increased');
     $ret = $driver->get_page_source();
     ok($ret =~ m/^<html/i, 'Received page source');
     eval {$driver->set_implicit_wait_timeout(20001);};