Fix flatMap types for Kefir

[mAAdhaTTah]

The error type should get combined into the resulting Observable,
rather than being replaced as it is now. merge & concat do
this correctly already.

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• Test the change in your own code. (Compile and run.)
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• 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: https://github.com/kefirjs/kefir/blob/master/kefir.js.flow#L129-L134
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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]

@mAAdhaTTah Thank you for submitting this PR!

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.

---

Diagnostic Information: What the bot saw about this PR

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[typescript-bot]

🔔 @AyaMorisawa @HitoriSensei - 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.

[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	#44634	diff
Batch compilation
Memory usage (MiB)	116.9	127.5	+9.1%
Type count	28019	29933	+7%
Assignability cache size	40630	40758	0%
Language service
Samples taken	764	786	+3%
Identifiers in tests	764	786	+3%
getCompletionsAtPosition
Mean duration (ms)	593.3	598.2	+0.8%
Mean CV	8.4%	9.1%
Worst duration (ms)	937.0	922.4	-1.6%
Worst identifier	x	x
getQuickInfoAtPosition
Mean duration (ms)	592.6	599.2	+1.1%
Mean CV	8.4%	9.1%	+9.2%
Worst duration (ms)	858.0	919.7	+7.2%
Worst identifier	prev	constant

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

[typescript-bot]

@mAAdhaTTah Unfortunately, this pull request currently has a merge conflict 😥. Please update your PR branch to be up-to-date with respect to master. Have a nice day!

[danger-public]

Inspecting the JavaScript source for this package found some properties that are not in the .d.ts files.
The check for missing properties isn't always right, so take this list as advice, not a requirement.

kefir (unpkg)

was missing the following properties:

1. dissableDeprecationWarnings
2. Kefir

Generated by 🚫 dangerJS against 5ee41e2

[typescript-bot]

@sandersn Thank you for reviewing this PR! The author has pushed new commits since your last review. Could you take another look and submit a fresh review?