fix(schematics): add comma before devtools for empty imports

[timdeschryver]

PR Checklist

Please check if your PR fulfills the following requirements:

• The commit message follows our guidelines: https://github.com/ngrx/platform/blob/master/CONTRIBUTING.md#commit
• Tests for the changes have been added (for bug fixes / features)
• Documentation has been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

[x] Bugfix
[ ] 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?

@LayZeeDK encountered this issue while using the schematics to scaffold a new project.
There's an missing , between the the StoreModule and StoreDevToolsModule.

@NgModule({
  imports: [
  StoreModule.forRoot(reducers, {
      metaReducers, 
      runtimeChecks: {
        strictStateImmutability: true,
        strictActionImmutability: true,
      },
    })!environment.production ? StoreDevtoolsModule.instrument() : []]
})
export class SharedDataAccessModule {}

What is the new behavior?

@NgModule({
  imports: [
  StoreModule.forRoot(reducers, { metaReducers }),
   !environment.production ? StoreDevtoolsModule.instrument() : []]
})
export class SharedDataAccessModule {}

Does this PR introduce a breaking change?

[ ] Yes
[x] No

Other information

While I was in the file, I also noticed the runtime checks.
These could also be removed because they're enabled by default.

[timdeschryver]

I also removed the runtime checks as these are enabled now.

[ngrxbot]

Preview docs changes for a385a78 at https://previews.ngrx.io/pr2542-a385a786/

[brandonroberts]

@timdeschryver if you'll rebase on master for the latest CI changes, we can go ahead and land it.

[timdeschryver]

@brandonroberts done!