Migrate to TypeScript version 3, fix MariaDB tests & use Github Actions

[LoicPoullain]

Issue

• The new version of class-validator, version 0.10.2, only supports TS@v3 (type unknown required). This makes the build of @foal/typestack fail with TS@v2.
• MariaDB unit tests actually test MySQL database since the default port 3306 is used.
• For some reason, the Travis pipeline is not triggered anymore when pushing a commit to a PR. It seems that FoalTS project is not detected anymore on Travis website.

Solution and steps

Starting from v1.3.0, FoalTS will only support TS@3.5 and beyond. This should not break current applications because most of them use TS@3.5 and beyond and the others that use TS@2.9 will only need to run npm run typescript@3 to go to the new version without breaking changes (TS@3 is highly compatible with TS@2.9).

• Build the packages with TypeScript 3.
• Make MariaDB tests use the right database.
• Set up a new CI pipeline with Github Actions (beta).

Checklist

• Add/update/check docs (code comments and docs/ folder).
• Add/update/check tests.
• Update/check the cli generators.

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (v1-3-0@c072945). Click here to learn what that means.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             v1-3-0     #557   +/-   ##
=========================================
  Coverage          ?   99.57%           
=========================================
  Files             ?       88           
  Lines             ?     1636           
  Branches          ?      371           
=========================================
  Hits              ?     1629           
  Misses            ?        7           
  Partials          ?        0

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