feat(lib): use TestBed.get if .inject falsy - back compatibility (#283)

[Coffee-Tea]

PR Checklist

Please check if your PR fulfills the following requirements:

• The commit message follows our guidelines: https://github.com/ngneat/spectator/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?
Backward compatibility change.
Allow to use 5.x lib version for Angular version less than v9.
Keep to use for Angular v9 as is.

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

What is the current behavior?

Issue Number: #283

What is the new behavior?

You can continue using the latest version of Spectator in you Angular projects with version less than 9 (e.g. 7, 8 etc.)

Does this PR introduce a breaking change?

[ ] Yes
[x] No

Other information

[NetanelBasal]

You need to update the peerDependencies.

[NetanelBasal]

This doesn't include v9. You need to use a range.

[NetanelBasal]

"typescript": ">= 2.8.0"

[Coffee-Tea]

let me check with this version of typescript,
I haven't checked it and not sure there are no new typescript features that are used in code which will not work with 2.8.0.

I will update you

[Coffee-Tea]

@NetanelBasal I would put "typescript": ">= 3.5.3" or smth like that b/c there are a bunch of errors when using 2.8.0. Actually, 3.5.3 was used as dependency in the root package.json:
e13c955#diff-b9cfc7f2cdf78a7f4b91a753d10865a2L77

Here is a part of errors I'm getting with 2.8.0:

Please confirm

[NetanelBasal]

This was the lastest version before we released v5:

spectator/projects/spectator/package.json

Line 35 in 5c98661

"typescript": ">= 2.8.0"

[Coffee-Tea]

@NetanelBasal yes you're right, but what is goal of peerDependencies? Maybe I'm wrong but should not we specify versions which gonna work with other specified peerDependencies versions?
I assume that it was wrong with >= 2.8.0 but if you're ok I will get back to it.

[Coffee-Tea]

I've used 8.2.0, my bad, but even typescript 3.0.0 was not working with 8.2.0.
Angular 8.2.0 was properly working with typescript 3.5.0

[Coffee-Tea]

Let me check 2.8.0 with 8.0.0

[Coffee-Tea]

Doesn't work for me trying 2.8.0 with 8.0.0,
also 8.0.0 angular is using 3.4.2 version https://github.com/angular/angular/blob/38a7e2a775d2c3495a8574dde7d1a7106dd0ae04/package.json#L108

so I'm really unsure in 2.8.0 but pushed it. It doesn't break anything, just seems to be smth like disinformation.

[NetanelBasal]

The TS version depends on your Angular version.

[Coffee-Tea]

Yes, that what I mean, and I'm not sure that TS 2.8.0 is compatible with Angular 8.0.0 :)