[workerpool] Ensure that the promise typing is PromiseLike

[forivall]

Please fill in this template.

• Use a meaningful title for the pull request. Include the name of the package modified.
• Test the change in your own code. (Compile and run.)
• Add or edit tests to reflect the change. (Run with npm test.)
• Follow the advice from the readme.
• Avoid common mistakes.
• Run npm run lint package-name (or tsc if no tslint.json is present).

Select one of these and delete the others:

If changing an existing definition:

• Provide a URL to documentation or source code which provides context for the suggested changes: N/A, Add promises-aplus tests for the promise library josdejong/workerpool#159 (it conforms to the standard promiselike type definition at least, so my changes are valid)
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• Include tests for your changes
• If you are making substantial changes, consider adding a tslint.json containing { "extends": "dtslint/dt.json" }. If for reason the any rule need to be disabled, disable it for that line using // tslint:disable-next-line [ruleName] and not for whole package so that the need for disabling can be reviewed.

[typescript-bot]

👋 Hi there! I’ve run some quick measurements against master and your PR. These metrics should help the humans reviewing this PR gauge whether it might negatively affect compile times or editor responsiveness for users who install these typings.

Let’s review the numbers, shall we?

Comparison details 📊

	master	#45399	diff
Batch compilation
Memory usage (MiB)	66.7	66.3	-0.5%
Type count	9327	9417	+1%
Assignability cache size	1783	1798	+1%
Language service
Samples taken	176	179	+2%
Identifiers in tests	176	179	+2%
getCompletionsAtPosition
Mean duration (ms)	356.7	358.1	+0.4%
Mean CV	10.2%	9.8%
Worst duration (ms)	422.2	431.1	+2.1%
Worst identifier	nodeWorker	nodeWorker
getQuickInfoAtPosition
Mean duration (ms)	356.4	361.3	+1.4%
Mean CV	9.9%	10.4%	+4.8%
Worst duration (ms)	423.6	449.0	+6.0%
Worst identifier	wp	nodeWorker

It looks like nothing changed too much. I won’t post performance data again unless it gets worse.

[typescript-bot]

@forivall Thank you for submitting this PR!

This is a live comment which I will keep updated.

Code Reviews

Because you edited one package and updated the tests (👏), I can help you merge this PR once someone else signs off on it.

Status

• ✅ No merge conflicts
• ✅ Continuous integration tests have passed
• ❌ Most recent commit is approved by type definition owners, DT maintainers or others

Once every item on this list is checked, I'll ask you for permission to merge and publish the changes.

Inactive

This PR has been inactive for 11 days — waiting for a DT maintainer!

---

Diagnostic Information: What the bot saw about this PR

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[typescript-bot]

🔔 @Alorel @sgkim126 - please review this PR in the next few days. Be sure to explicitly select Approve or Request Changes in the GitHub UI so I know what's going on.

[elibarzilay]

Re-ping @Alorel @sgkim126