Add support for 'amazon' platform_family

[pazmarianoj]

In attributes default.rb 'amazon' is not listed as platform_family option. This should be included as an alternative of 'rhel' or 'fedora' in order to properly define other attributes that are coupled to it.

cookbook-php-fpm/attributes/default.rb

Line 2 in f5cb498

when 'rhel', 'fedora'

I'm opening a PR because of this.