chore(release): 1.6.0 [skip ci]

# [1.6.0](https://github.com/saltstack-formulas/php-formula/compare/v1.5.1...v1.6.0) (2022-03-14)

### Continuous Integration

* update linters to latest versions [skip ci] ([8befefcf](https://github.com/saltstack-formulas/php-formula/commit/8befefcfbe50378691cf199f900cf2ca8ba4339f))
* **gemfile:** allow rubygems proxy to be provided as an env var [skip ci] ([4f544745](https://github.com/saltstack-formulas/php-formula/commit/4f5447451d28137f488bcb20313d6c30fe3e9dd8))
* **kitchen+ci:** update with `3004` pre-salted images/boxes [skip ci] ([def69936](https://github.com/saltstack-formulas/php-formula/commit/def69936b47bfd0e65e521a3b2629b591e2a11ca))
* **kitchen+ci:** update with latest CVE pre-salted images [skip ci] ([ded03de0](https://github.com/saltstack-formulas/php-formula/commit/ded03de05e777a4c3b0a1aad8de650470c244d6a))
* **kitchen+gitlab:** update for new pre-salted images [skip ci] ([2e98aed8](https://github.com/saltstack-formulas/php-formula/commit/2e98aed831e0adcfdc7f34df7c29529614a4ce0e))
* **vagrant:** replace FreeBSD 12.2 with 12.3 [skip ci] ([4e5af987](https://github.com/saltstack-formulas/php-formula/commit/4e5af9875abd9e4149db2d3e10c9f6dfcca435f2))

### Features

* **modules:** add `xmlrpc` and `xmlreader` as FreeBSD `xml` module ([67e565f5](https://github.com/saltstack-formulas/php-formula/commit/67e565f5e2ce83c26a79267f25317e6e4340a73e))

### Tests

* **system:** add `build_platform_codename` [skip ci] ([f1592024](https://github.com/saltstack-formulas/php-formula/commit/f1592024d507873415debcdc03aa2c885af2e4cf))