Broken link in CODE_OF_CONDUCT.md

[YexuanXiao]

The last link on line 107 of docs/CODE_OF_CONDUCT.md is broken because commit 923b3ec accidentally deleted a slash, and the correct link is https://www.un.org/en/genocideprevention/documents/UN%20Strategy%20and%20Plan%20of%20Action%20on%20Hate%20Speech%2018%20June%20SYNOPSIS.pdf.

beman/docs/code_of_conduct.md

Line 107 in 80d207f

Important examples include, but are not limited to, [sexual and gender-based violence and/or harassment](https://hr.un.org/sites/hr.un.org/files/SEA%20Glossary%20%20%5BSecond%20Edition%20-%202017%5D%20-%20English_0.pdf), [hate crimes](https://hatecrime.osce.org/), and [hate speech](https://www.un.org/en/genocideprevention/documentsUN%20Strategy%20and%20Plan%20of%20Action%20on%20Hate%20Speech%2018%20June%20SYNOPSIS.pdf).

[neatudarius]

@mihneagrigore, please check all URLs in this repo (both external and relative files).