Fix bug with inserting links and undoing things.

src/js/simplemde.js

@@ -795,8 +795,9 @@ function _replaceSelection(cm, active, startEnd, url) {
 	var text;
 	var start = startEnd[0];
 	var end = startEnd[1];
-	var startPoint = cm.getCursor("start");
-	var endPoint = cm.getCursor("end");
+	var startPoint = {}, endPoint = {};
+	Object.assign(startPoint, cm.getCursor("start"));
+	Object.assign(endPoint, cm.getCursor("end"));
 	if(url) {
 		end = end.replace("#url#", url);
 	}
@@ -2025,4 +2026,4 @@ SimpleMDE.prototype.toTextArea = function() {
 	}
 };
 
-module.exports = SimpleMDE;
+module.exports = SimpleMDE;