Remove use of deprecated React.PropTypes

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

src/components/views/rooms/ReadReceiptMarker.js

@@ -18,6 +18,7 @@ limitations under the License.
 
 const React = require('react');
 const ReactDOM = require('react-dom');
+import PropTypes from 'prop-types';
 
 const sdk = require('../../../index');
 
@@ -40,35 +41,35 @@ module.exports = React.createClass({
 
     propTypes: {
         // the RoomMember to show the RR for
-        member: React.PropTypes.object.isRequired,
+        member: PropTypes.object.isRequired,
 
         // number of pixels to offset the avatar from the right of its parent;
         // typically a negative value.
-        leftOffset: React.PropTypes.number,
+        leftOffset: PropTypes.number,
 
         // true to hide the avatar (it will still be animated)
-        hidden: React.PropTypes.bool,
+        hidden: PropTypes.bool,
 
         // don't animate this RR into position
-        suppressAnimation: React.PropTypes.bool,
+        suppressAnimation: PropTypes.bool,
 
         // an opaque object for storing information about this user's RR in
         // this room
-        readReceiptInfo: React.PropTypes.object,
+        readReceiptInfo: PropTypes.object,
 
         // A function which is used to check if the parent panel is being
         // unmounted, to avoid unnecessary work. Should return true if we
         // are being unmounted.
-        checkUnmounting: React.PropTypes.func,
+        checkUnmounting: PropTypes.func,
 
         // callback for clicks on this RR
-        onClick: React.PropTypes.func,
+        onClick: PropTypes.func,
 
         // Timestamp when the receipt was read
-        timestamp: React.PropTypes.number,
+        timestamp: PropTypes.number,
 
         // True to show twelve hour format, false otherwise
-        showTwelveHour: React.PropTypes.bool,
+        showTwelveHour: PropTypes.bool,
     },
 
     getDefaultProps: function() {