Feature/add GitHub actions

[SuperITMan]

Please check if the PR fulfills these requirements

• [X] The commit message follows our guidelines: https://github.com/HackedByChinese/ng2-idle/blob/master/CONTRIBUTING.md#pr
• [ ] Tests for the changes have been added (for bug fixes / features)
• [X] Docs have been added / updated (for bug fixes / features)

What kind of change does this PR introduce? (check one with "x")

[ ] Bugfix
[X] Feature
[ ] Code style update (formatting, local variables)
[X] Refactoring (no functional changes, no api changes)
[X] Build related changes
[X] CI related changes
[ ] Other... Please describe:

What is the current behavior? (You can also link to an open issue here)

1. CI depends on Travis CI which is no longer available.

   

2. "package-lock.json" file is in v1 (for npm < 7.x).

3. Some links in documentation + package.json are pointing to old https://github.com/HackedByChinese.

What is the new behavior?

1. Switch from Travis CI to GitHub Actions.

2. "package-lock.json" updated to v2 (npm >= 7.x)

3. Links updated to https://github.com/moribvndvs/ng2-idle

Does this PR introduce a breaking change? (check one with "x")

[ ] Yes
[X] No

If this PR contains a breaking change, please describe the impact and migration path for existing applications: ...

Other information:

[SuperITMan]

Hey @bh3605 @moribvndvs

Could you have a look to my PR which drops Travis in favor of GitHub Actions? 😊