docs(changelog): fix example import statement

[jspieker]

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

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
[x] Documentation content changes
[ ] Other... Please describe:

What is the current behavior?

The example import statement wrongfully shows an import of ofType from @ngrx/store.

What is the new behavior?

The example import now imports from @ngrx/effects.

Does this PR introduce a breaking change?

[ ] Yes
[x] No

Other information

[coveralls]

Coverage remained the same at 89.515% when pulling 954629d on jspieker:patch-2 into 01ff157 on ngrx:master.

[ngrxbot]

Preview docs changes for 954629d at https://previews.ngrx.io/pr1569-954629d/

[timdeschryver]

The CHANGELOG is generated by the commits we push, thus we, unfortunately, can't update the CHANGELOG.

The migration on ngrx.io is correct.