Move to circle 2.0

Move to circle 2.0

adds support for apex classes codeclimate#26 (codeclimate#29)

Currently, Salesforce developers cannot use CodeClimate despite CodeClimate having PMD as a plugin. This is because the PMD plugin filters out all files that are not Java (.java). This patch allows for the Apex class extension to be processed as well (.cls).

Related to codeclimate#26

Merge pull request codeclimate#28 from codeclimate/sl/update-pmd

Upgrade codeclimate-pmd

Fix readup (codeclimate#25)

* Related to https://github.com/codeclimate/app/issues/5817
* Remove bogus markdown - intended for PMD internal use only (codeclimate#25)

Upgrade PMD to version 6.0.1 (codeclimate#23)

* Upgrade PMD to version 6

* Adjust regression suite as the new version has different output values

* Use new rules xml instead of group name, as they became incompatible

* Speedup analysis with builtin cache

* Redirect warnings to stderr

* Hardcode ruleset as runtime directory changes

Adjust analysis config (codeclimate#24)

Use community submitted engine to check groovy code (codeclimate#22)

Replace default xml rules with rule names (codeclimate#20)

Allow rules string as a configuration alternative (codeclimate#19)