update links in readme

Author: huidongchen

README.md

@@ -49,9 +49,9 @@ You should see the notebook open in your browser.
 Tutorial
 --------
 
-* Example for scRNA-seq: [1.1.STREAM_scRNA-seq (on 2D plane).ipynb](https://nbviewer.jupyter.org/github/pinellolab/STREAM/blob/master/tutorial/1.STREAM_scRNA-seq.ipynb?flush_cache=true)
+* Example for scRNA-seq: [1.1.STREAM_scRNA-seq (on 2D plane).ipynb](https://nbviewer.jupyter.org/github/pinellolab/STREAM/blob/master/tutorial/1.1.STREAM_scRNA-seq%20%28on%202D%20plane%29.ipynb?flush_cache=true)
 
-* Example for scRNA-seq: [1.2.STREAM_scRNA-seq (in 3D space).ipynb](https://nbviewer.jupyter.org/github/pinellolab/STREAM/blob/master/tutorial/1.STREAM_scRNA-seq.ipynb?flush_cache=true)
+* Example for scRNA-seq: [1.2.STREAM_scRNA-seq (in 3D space).ipynb](https://nbviewer.jupyter.org/github/pinellolab/STREAM/blob/master/tutorial/1.2.STREAM_scRNA-seq%20%28in%203D%20space%29.ipynb?flush_cache=true)
 
 * Example for *mapping* feature: [2.STREAM_mapping.ipynb](https://nbviewer.jupyter.org/github/pinellolab/STREAM/blob/master/tutorial/2.STREAM_mapping.ipynb?flush_cache=true)