Deprecation array property warning with PHP_CodeSniffer 3.13.0

[mikemanger]

This was deprecated in 3.3.0 and hard deprecated in 3.13.0.

DEPRECATED: Passing an array of values to a property using a comma-separated string
was deprecated in PHP_CodeSniffer 3.3.0. Support will be removed in PHPCS 4.0.0.
The deprecated syntax was used for property "functionWhitelist"
for sniff "PHPCompatibility.Extensions.RemovedExtensions".

[jrfnl]

@mikemanger Thanks for reporting this. PR #64 should fix it ;-)