Fix matthiasmullie#301 calc() not followed by end of line or semicolo… …n not correctly matched

Implode swap parameter order for PHP-7.4 support. 

php-cs-fixer 

Don't iterate over positions that have already been unset Fixes matthiasmullie#245

Run tests with Docker 

Add test for matthiasmullie#227 

Add 7.2 to build matrix 

Leave calc expressions alone when stripping units off of 0 Fixed matthiasmullie#217

Fix PHP5.3 compatibility Yet another ugly workaround... Fixes matthiasmullie#208

Regexes can also start in array Fixes matthiasmullie#209