Adding mendeley

[bonniewhy]

Issue:
#1853

Checklist

• I updated the JSON data in _data/simple-icons.json
• I optimized the icon with SVGO or SVGOMG
• The SVG viewbox is 0 0 24 24

Description

The hex value was provided in the issue, and looking around on the website and the Wikipedia page, that looks like it matches. The logo link that was provided was already an SVG, so I didn't have to manually vectorize it.

[birjj]

Thanks for the PR, and for following our contribution guidelines! That is very much appreciated.
I do have a couple things to ask before I get this merged in:

• Could you update the "source" URL to https://www.mendeley.com/? It's a bit arbitrary, but we usually prefer having as general of a URL as possible if the SVG itself is easy enough to extract (in this case it seems to be available in the header of their website). That way the link doesn't break if they decide to update where their logo is located in their hosting structure.
• It looks like the viewbox is just a tiny bit off what we want - the PR uses viewBox="0 0.016 24 24", which makes our build system complain. Could you update that? Given the tiny difference it should be enough to just update the text directly, without bothering with the path data.
• And finally - pretty nonsensical, but since I'm sending you off to do edits anyway: based on the CSS of https://dev.mendeley.com/ it looks like the official color is #9D1620. Could you please update that too?

Other than those very minor details, good work on this PR so far!

[bonniewhy]

Hopefully that's better! Let me know if anything else needs fixing. :)

[birjj]

👍 Looks good! Thanks a lot for the contribution and the update!