Fix the assignment 2nd phase deadline.

Author: janpgit

docs/index.html

@@ -130,8 +130,9 @@ <h2><a name="practices">Practices and class assignments</a></h2>
 the end of the Winter semester, ie. Sunday 23:59, January 12, 2020.  All
 examples shown in the assignment above must work as expected.
 
-<p>The second phase must be finished and handed over to us before the end of the
-Summer semester, ie. by Tuesday 23:59, June 30, 2019.
+<p>The second phase must be finished and handed over to us before the
+examination period for the Summer semester starts, i.e. by Sunday 23:59, May 24,
+2019.
 
 <p>If you need to finish your semester earlier (that may apply to Erasmus
 students), you need to finish the 2nd assignment in full before that.