Docker container for testing META6.json in the ecosystem

Test container, based on Alpine, with OpenSSL⁠ and the rest of the modules needed for testing Perl 6 ecosystem modules, basically Test::Meta. It probably does not make a lot of sense anywhere else, except if you want to also test correctness of the META6.json files in Perl 6 distributions. Check it out here⁠

Use in Travis

language:
  - minimal

services:
  - docker

install:
  - docker pull jjmerelo/perl6-test-ecosystem
  - docker images # This is just for the show

script: docker run -e TRAVIS_COMMIT_RANGE="HEAD^1...HEAD" -t -v  $TRAVIS_BUILD_DIR:/test jjmerelo/perl6-test-ecosystem

docker images is not needed, but it will show you the version it is going to use for building.