Log Message:
devel/php-gearman: update to 2.0.6

Update php-gearman package to 2.0.6.

pkgsrc change:
* Switch GitHub repository to php's.
* Allow build with PHP 7.2 and 7.3.

Version 2.0.6 (2019-09-05)
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- fixing issue with double calling of zval_dtor in set fail callback