Use hrtime instead of microtime in Redis facade

[xwiz]

Don't exactly know if categorize this as a bug or feature but according to the PHP docs, https://www.php.net/manual/en/function.hrtime.php The new hrtime is better especially in virtualized environments.

For Redis Connection class which is performance sensitive, it would be great to have this switch.

There's also a related issue here: guzzle/guzzle#2214