Do not flip five or more consecutive values

Update the 'four value notation' tests to feature an actually
valid CSS rule instead of just a single property as the new
flip rule needs to be able to tell where the end of a declaration
is (through semi colon or brace).

The regex could be changed to also allow '$' (end of string) in
additino to ';' and '}', but it seems sensible to just make the
sample input in the test suite valid CSS.

Inspired by a patch from Bartosz Dziewoński to the PHP-port of
CSSJanus that ships with MediaWiki:
* https://github.com/wikimedia/mediawiki-core/blob/1.23.3/includes/libs/CSSJanus.php
* https://github.com/wikimedia/mediawiki-core/commit/3eaad66d63