fixed image links in quick start

doc/quick-start.md

 
 Here is how it might look when we run the app and navigate to editor page:
 
-<img src="https://github.com/memspace/zefyr/raw/gitbook/assets/quick-start-rec-01.gif" width="600">
+<img src="https://github.com/memspace/zefyr/raw/master/assets/quick-start-rec-01.gif" width="600">
 
 ### 04. Save document to JSON file
 
 
 Now we can reload our app, hit "Save" button and see the snack bar.
 
-<img src="https://github.com/memspace/zefyr/raw/gitbook/assets/quick-start-rec-02.gif" width="600">
+<img src="https://github.com/memspace/zefyr/raw/master/assets/quick-start-rec-02.gif" width="600">
 
 ### 05. Load document from JSON file
 
 
 If we save changes now and reload the app we should see something like this:
 
-<img src="https://github.com/memspace/zefyr/raw/gitbook/assets/quick-start-rec-03.gif" width="600">
+<img src="https://github.com/memspace/zefyr/raw/master/assets/quick-start-rec-03.gif" width="600">
 
 Note that in your tests you'll likely not notice any loading animation at all.
 This is because reading a tiny file from disk is too fast. For the above