Add contributors to the 21st release blog article

Author: anatoliykmetyuk

docs/blog/_posts/2019-12-20-21th-dotty-milestone-release.md

@@ -312,7 +312,38 @@ Thank you to all the contributors who made this release possible!
 According to `git shortlog -sn --no-merges 0.20.0-RC1..0.21.0-RC1` these are:
 
 ```
-    <todo>
+   176  Martin Odersky
+   171  Bryan Abate
+    88  Nicolas Stucki
+    81  Jamie Thompson
+    44  noti0na1
+    29  Anatolii
+    28  bishabosha
+    23  Antoine Brunner
+    19  Guillaume Martres
+    10  Aleksander Boruch-Gruszecki
+     8  Guillaume Raffin
+     6  Olafur Pall Geirsson
+     5  Sébastien Doeraene
+     4  Aggelos Biboudis
+     4  Liu Fengyun
+     4  Paolo G. Giarrusso
+     3  Andrea Mocci
+     3  Martijn Hoekstra
+     2  Ben Elliott
+     2  Patrik Mada
+     2  Rafal Piotrowski
+     2  odersky
+     1  Markus Kahl
+     1  Richard Beddington
+     1  Vlastimil Dort
+     1  Anatolii Kmetiuk
+     1  Raphael Jolly
+     1  Lucas
+     1  Nikita Eshkeev
+     1  Brian Wignall
+     1  Olivier Blanvillain
+     1  张志豪
 ```
 
 If you want to get your hands dirty and contribute to Dotty, now is a good time to get involved!