feat(package): migrate to ng12

[sqrter]

BREAKING CHANGE: ng12

** PR Checklist Please check if your PR fulfills the following requirements:

• [x] The commit message follows our guidelines: https://github.com/fulls1z3/ngx-meta/blob/master/CONTRIBUTING.md#commit
• [x] Tests for the changes have been added (for bug fixes / features)
• [x] Docs have been added / updated (for bug fixes / features)

** PR Type What kind of change does this PR introduce?

[ ] Bugfix
[ ] Feature
[ ] Code style update (formatting, local variables)
[ ] Refactoring (no functional changes, no api changes)
[ ] Build related changes
[ ] CI related changes
[ ] Documentation content changes
[ x] Other... Please describe: Add support of Angular 12

** What is the current behavior? https://github.com/fulls1z3/ngx-meta/issues/210

Issue Number: 210

** What is the new behavior?

** Does this PR introduce a breaking change?

[ x] Yes
[ ] No

** Other information

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[codecov[bot]]

Codecov Report

Merging #214 (5c91333) into master (6329569) will increase coverage by 0.00%. The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #214   +/-   ##
=======================================
  Coverage   98.75%   98.76%           
=======================================
  Files           7        7           
  Lines         161      162    +1     
  Branches       47       50    +3     
=======================================
+ Hits          159      160    +1     
  Misses          2        2           

Impacted Files	Coverage Δ
packages/@ngx-meta/core/src/index.ts	100.00% <0.00%> (ø)

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[RomainMarecat]

When will it be merged and released ? Your lib block my migration to ng 12, i hope you merge soon soon :)

[fulls1z3]

@sqrter @RomainMarecat need help with these PR's, especially with ng-packagr is failing. once done aim is first to ng 10 and then eventually to ng11 and ng12 (supporting all intermediate versions)

• https://github.com/fulls1z3/ngx-meta/pull/216
• https://github.com/fulls1z3/ngx-config/pull/169
• https://github.com/fulls1z3/ngx-cache/pull/141
• https://github.com/fulls1z3/ngx-auth/pull/135

and finally we're showcasing it on https://github.com/fulls1z3/universal/pull/755