Merge pull request rbenv#1306 from olivierlacan/2-7-0-preview1

Add CRuby 2.7.0-preview1

20190423

Bump up to 20190401.

Bump version to v20190320

bump version to v20190314

Bump version to 20190130

Bump version to 20181225

Bump version to 20181207

Added definition of Ruby 2.6.0 preview3

Merge pull request rbenv#1244 from devinrm/dm-bump-version-to-2018-10-19

Bump version to 20181019