Prepare for release 7.3.3

Author: thijskh

ChangeLog

@@ -1,7 +1,7 @@
 DOMjudge Programming Contest Judging System
 
-Version 7.3.3 - DEV
--------------------
+Version 7.3.3 - 5 April 2021
+----------------------------
  - Fix single problem API action for non-jury members.
  - Fix reversed submission diff output.
  - Fix for browser swallowing newlines in output listings.

README.md

@@ -4,7 +4,7 @@ DOMjudge
 [![Coverity Scan Status](https://img.shields.io/coverity/scan/671.svg)](https://scan.coverity.com/projects/domjudge)
 [![LGTM alerts](https://img.shields.io/lgtm/alerts/g/DOMjudge/domjudge.svg?logo=lgtm&logoWidth=18)](https://lgtm.com/projects/g/DOMjudge/domjudge/alerts/)
 
-This is the Programming Contest Jury System "DOMjudge" version 7.3.2DEV
+This is the Programming Contest Jury System "DOMjudge" version 7.3.3
 
 DOMjudge is a system for running a programming contest, like the
 ICPC regional and world championship programming contests.