fix broken link in no-is-mounted.md

[bastiendmt]

Hi !

The link in no-is-mounted is broken.

I was able to find the article in the legacy docs.

This PR fixes the link

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 97.58%. Comparing base (63aceff) to head (217185b).
Report is 2 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3841      +/-   ##
==========================================
- Coverage   97.67%   97.58%   -0.09%     
==========================================
  Files         136      133       -3     
  Lines        9969     9957      -12     
  Branches     3693     3693              
==========================================
- Hits         9737     9717      -20     
- Misses        232      240       +8     

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[ljharb]

sigh, facebook broke a bunch of links.

there's a dozen other facebook.github.io links in the repo; can you fix all of them?

[bastiendmt]

sigh, facebook broke a bunch of links.

there's a dozen other facebook.github.io links in the repo; can you fix all of them?

Yeah weird that they did not migrate their blog posts.

I fixed other links. I was able to replace one with the newer docs.
Also one link is missing even in the legacy docs so I completely removed the link

[ljharb]

Suggested change

	When using a boolean attribute in JSX, you can set the attribute value to `true` or omit the value.
	When using a [boolean attribute in JSX](https://web.archive.org/web/20160607204033/http://facebook.github.io/react/docs/jsx-in-depth.html#boolean-attributes), you can set the attribute value to `true` or omit the value.

let's use the original material this linked to instead.