bpo-30824: Add mimetype for .json (#3048)

diff --git a/Lib/mimetypes.py b/Lib/mimetypes.py
index 3d68694..5919b45 100644
--- a/Lib/mimetypes.py
+++ b/Lib/mimetypes.py
@@ -439,6 +439,7 @@
         '.jpeg'   : 'image/jpeg',
         '.jpg'    : 'image/jpeg',
         '.js'     : 'application/javascript',
+        '.json'   : 'application/json',
         '.ksh'    : 'text/plain',
         '.latex'  : 'application/x-latex',
         '.m1v'    : 'video/mpeg',