Remove use of deprecated React.PropTypes

Replace all uses of React.PropTypes with PropTypes and importing PropTypes from
'prop-types'.

src/components/views/groups/GroupRoomTile.js

@@ -66,7 +66,7 @@ const GroupRoomTile = React.createClass({
 });
 
 GroupRoomTile.contextTypes = {
-    matrixClient: React.PropTypes.instanceOf(MatrixClient).isRequired,
+    matrixClient: PropTypes.instanceOf(MatrixClient).isRequired,
 };