Updated minimum PHP version in README.md.
Updated minimum PHP version in README.md.

Symfony/YAML requires PHP 5.3.3 (and Composer requires 5.3.2, so there is not a great compatibility loss by the recent switch away from the PECL extension for YAML).

mikk150/PHPCI,corretgecom/PHPCI,dwolke/phpci,nelsonyang0710/PHPCI,leadermt/PHPCI,andreustimm/PHPCI,gdseller/PHPCI,Adirelle/PHPCI,dwolke/phpci,SamMousa/PHPCI,corpsee/php-censor,mindteam/PHPCI,mseshachalam/PHPCI,andreustimm/PHPCI,Coderockr/PHPCI,onedal88/PHPCI,keradus/PHPCI,cooperaj/PHPCI,corpsee/php-censor,corretgecom/PHPCI,mseshachalam/PHPCI,rafaelang/PHPCI,leadermt/PHPCI,php-censor/php-censor,nevernet/PHPCI,mikebronner/PHPCI,mindteam/PHPCI,jimmycleuren/PHPCI,juanf/PHPCI,tankist/PHPCI,steverobbins/PHPCI,Adirelle/PHPCI,juanf/PHPCI,mikebronner/PHPCI,SamMousa/PHPCI,corpsee/php-censor,andreustimm/PHPCI,steverobbins/PHPCI,ojengwa/PHPCI,mavimo/PHPCI,nelsonyang0710/PHPCI,jimmycleuren/PHPCI,cooperaj/PHPCI,Lechus/PHPCI,nevernet/PHPCI,php-censor/php-censor,ronanchilvers/PHPCI,zilionis/PHPCI,Lechus/PHPCI,dwolke/phpci,zilionis/PHPCI,mikk150/PHPCI,SamMousa/PHPCI,laszlof/PHPCI,LewisW/PHPCI,gdseller/PHPCI,mehulsbhatt/PHPCI,seshurajup/PHPCI,Topface/PHPCI,keradus/PHPCI,nevernet/PHPCI,keradus/PHPCI,laszlof/PHPCI,steverobbins/PHPCI,Topface/PHPCI,LewisW/PHPCI,cooperaj/PHPCI,seshurajup/PHPCI,mehulsbhatt/PHPCI,nelsonyang0710/PHPCI,Adirelle/PHPCI,mikebronner/PHPCI,onedal88/PHPCI,laszlof/PHPCI,chtombleson/PHPCI,tankist/PHPCI,juanf/PHPCI,gdseller/PHPCI,mseshachalam/PHPCI,mikk150/PHPCI,chtombleson/PHPCI,corretgecom/PHPCI,chtombleson/PHPCI,mindteam/PHPCI,Topface/PHPCI,LewisW/PHPCI,Block8/PHPCI,onedal88/PHPCI,mavimo/PHPCI,leadermt/PHPCI,php-censor/php-censor,seshurajup/PHPCI,Coderockr/PHPCI,ojengwa/PHPCI,rafaelang/PHPCI,mavimo/PHPCI,Block8/PHPCI,ojengwa/PHPCI,ronanchilvers/PHPCI,tankist/PHPCI,ronanchilvers/PHPCI,ronanchilvers/PHPCI,wodka/PHPCI,rafaelang/PHPCI,Block8/PHPCI,Lechus/PHPCI,wodka/PHPCI,mehulsbhatt/PHPCI,Coderockr/PHPCI,jimmycleuren/PHPCI,zilionis/PHPCI