Add skeleton of 3.8 release blog post

source/blog/2018-06-25-rspec-3-8-has-been-released.md

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+---
+title: RSpec 3.8 has been released!
+author: Sam Phippen
+---
+
+RSpec 3.8 has just been released! Given our commitment to
+[semantic versioning](http://semver.org/), this should be an easy
+upgrade for anyone already using RSpec 3, but if we did introduce
+any regressions, please let us know, and we'll get a patch release
+out with a fix ASAP.
+
+RSpec continues to be a community-driven project with contributors
+from all over the world. This release includes over xxx commits and yyy
+merged pull requests from zzz different contributors!
+
+Thank you to everyone who helped make this release happen!
+
+## Notable Changes
+
+TODO: extract from changelogs.
+
+## Stats:
+
+TODO: generate
+
+
+## Docs
+
+### API Docs
+
+* [rspec-core](/documentation/3.8/rspec-core/)
+* [rspec-expectations](/documentation/3.8/rspec-expectations/)
+* [rspec-mocks](/documentation/3.8/rspec-mocks/)
+* [rspec-rails](/documentation/3.8/rspec-rails/)
+
+### Cucumber Features
+
+* [rspec-core](http://relishapp.com/rspec/rspec-core)
+* [rspec-expectations](http://relishapp.com/rspec/rspec-expectations)
+* [rspec-mocks](http://relishapp.com/rspec/rspec-mocks)
+* [rspec-rails](http://relishapp.com/rspec/rspec-rails)
+
+## Release notes:
+
+TODO: generate