Bump PHP version check in bootstrap code to v5.4+
Bump PHP version check in bootstrap code to v5.4+

fixes https://github.com/wp-cli/wp-cli/issues/5037
trepmal/wp-cli,rodrigoprimo/wp-cli,aaemnnosttv/wp-cli,aaemnnosttv/wp-cli,aaemnnosttv/wp-cli,rodrigoprimo/wp-cli,rodrigoprimo/wp-cli,trepmal/wp-cli,trepmal/wp-cli