Update link to qt homepage

Author: m-kuhn

README.md

@@ -7,7 +7,7 @@ May of 2002 and was established as a project on SourceForge in June of the same
 year. We've worked hard to make GIS software (which is traditionally expensive
 commercial software) a viable prospect for anyone with basic access to a
 Personal Computer.  QGIS currently runs on most Unix platforms, Windows, and OS
-X. QGIS is developed using the Qt toolkit (http://qt.digia.com) and C++.  This
+X. QGIS is developed using the Qt toolkit (http://qt.io) and C++.  This
 means that QGIS feels snappy to use and has a pleasing, easy to use graphical
 user interface.