Update links in README

Author: wojtekmaj

packages/react-date-picker/README.md

@@ -18,7 +18,7 @@ A date picker for your React app.
 
 A minimal demo page can be found in `sample` directory.
 
-[Online demo](http://projects.wojtekmaj.pl/react-date-picker/) is also available!
+[Online demo](https://projects.wojtekmaj.pl/react-date-picker/) is also available!
 
 ## Looking for a time picker or a datetime picker?