feat(package): migrate to ng9

[fulls1z3]

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

• The commit message follows our guidelines: https://github.com/fulls1z3/ngx-config/blob/master/CONTRIBUTING.md#commit
• Tests for the changes have been added (for bug fixes / features)
• 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)
[x] Build related changes
[ ] CI related changes
[ ] Documentation content changes
[ ] Other... Please describe:

** What is the current behavior?

Issue Number: N/A

** What is the new behavior?

** Does this PR introduce a breaking change?

[ ] Yes
[x] No

** Other information

BREAKING CHANGE

[codecov]

Codecov Report

Merging #161 into master will decrease coverage by 2.37%.
The diff coverage is 50.00%.

@@            Coverage Diff             @@
##           master     #161      +/-   ##
==========================================
- Coverage   97.97%   95.60%   -2.38%     
==========================================
  Files           9        9              
  Lines          99       91       -8     
  Branches       12       12              
==========================================
- Hits           97       87      -10     
- Misses          2        4       +2     

Impacted Files	Coverage Δ
packages/@ngx-config/core/src/config.module.ts	80.00% <50.00%> (-10.91%)	⬇️
packages/@ngx-config/core/src/config.pipe.ts	100.00% <0.00%> (ø)
packages/@ngx-config/core/src/config.loader.ts	100.00% <0.00%> (ø)
packages/@ngx-config/core/src/config.service.ts	100.00% <0.00%> (ø)
.../@ngx-config/http-loader/src/config.http-loader.ts	100.00% <0.00%> (ø)
...ngx-config/merge-loader/src/config.merge-loader.ts	100.00% <0.00%> (ø)

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[ghost]

Warnings are found on analyzing the commit ae8df83.

2 warnings:

• ⚠️ Goodcheck
• ⚠️ TSLint

We recommend to address them as possible, for example, update outdated dependencies, fix the tool's configuration, configure sider.yml, turn off unused tools, and so on.

If you are struggling with these errors or warnings, feel free to ask us via chat. 💬