doc: updates for better json generating

[Semigradsky]

E.g. for tracker.calls([fn][, exact]) from doc/api/assert.md we currently have:

The return.desc doesn't explain return type.

So I made a change:

- * Returns: {Function} that wraps `fn`.
+ * Returns: {Function} A function that wraps `fn`.

[nodejs-github-bot]

Review requested:

• [ ] @nodejs/crypto
• [ ] @nodejs/http
• [ ] @nodejs/loaders
• [ ] @nodejs/net
• [ ] @nodejs/test_runner

[ShogunPanda]

@aduh95 This looks fine to me in general. Do we have any tool that would be broken by this?

[nodejs-github-bot]

Landed in bf3971673593ebd3f1f65b2d15a717f0784379ff