docs: fix module import (#1930)

[pegaltier]

PR Checklist

Please check if your PR fulfills the following requirements:

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

PR Type

What kind of change does this PR introduce?

only doc

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

What is the current behavior?

Closes #1930

What is the new behavior?

Does this PR introduce a breaking change?

[ ] Yes
[X ] No

Other information

[ngrxbot]

Preview docs changes for f71e624 at https://previews.ngrx.io/pr1932-f71e624/

[timdeschryver]

There is another NgRxDataModule.forRoot at the bottom of the page, could you also catch that one please?

[ngrxbot]

Preview docs changes for de552f9 at https://previews.ngrx.io/pr1932-de552f9/