Update month

Author: leonardehrenfried

index.md

@@ -54,7 +54,7 @@ Helsinki
 Please register to attend by [filling out this form](https://docs.google.com/forms/d/e/1FAIpQLSdR363ujobEKi5g_cP96r6X4UVhGy2J7pyir5dbX-u9eQCJRg/viewform?usp=dialog)
 as it helps us to plan the event better.
 
-<b>Please register before 25th of September (registration will be available still after this deadline but
+<b>Please register before 25th of August (registration will be available still after this deadline but
 you might miss out on some social activity)</b>.
 
 ## Who will be there?