Change `$this` parameter in closure to `$that` to prevent memory leak.
Change `$this` parameter in closure to `$that` to prevent memory leak.

Using `$this` as a parameter name in a closure under PHP 7 causes a memory leak
under some specific circumstances which are present in this component.

Relevant PHP issue: https://bugs.php.net/bug.php?id=71737
More information: https://gist.github.com/jmalloc/e3db5842c2c4ab2a1edf

arnaud-lb/http-client