Prevent future dependency problems

[bessarabov]

Yesterday @JaSei has created pull request with fix of the dependency problem — #6

This problem appeared because cpan-api is activly developing and sometimes new deps appear in it. But this metacpan-docker project is trying to install the latest version of cpan-api (as well as other projects). And here lies the problem —metacpan-docker has deps for version cpan-api version 100 and it is tested to work with this version, but when version 200 appears it can be broken because is was never tested with this version.

I propose the following solution:

1. In every Dockerfile explicity specify the version of project that should be installed
2. Create versions for metacpan-docker projects and write in changelog what versions of projects are used in every version of metacpan-docker.

I'm thinking about version scheme. I like http://semver.org/ but it don't agree with the section "What should I do if I update my own dependencies without changing the public API?" — I would like to change the major version of metacpan-docker when change dependencies.

[oalders]

I'm sorry we never properly addressed this, @bessarabov. We are only using the compose setup for development, so I think it's easier to deal with dependencies every so often rather than hard coding in versions that need to be bumped.