DOC: Remove .ipynb suffix from "toctree"

sphinx-doc/sphinx#5756

doc/index.rst

@@ -7,18 +7,18 @@ was generated from Jupyter notebooks.
     :maxdepth: 3
     :glob:
 
-    installation.ipynb
-    usage.ipynb
-    markdown-cells.ipynb
-    code-cells.ipynb
-    raw-cells.ipynb
-    hidden-cells.ipynb
-    executing-notebooks.ipynb
-    prolog-and-epilog.ipynb
-    custom-formats.ipynb
+    installation
+    usage
+    markdown-cells
+    code-cells
+    raw-cells
+    hidden-cells
+    executing-notebooks
+    prolog-and-epilog
+    custom-formats
     subdir/*
-    a-normal-rst-file.rst
-    links.ipynb
+    a-normal-rst-file
+    links
 
 .. only:: html
 

doc/usage.ipynb

@@ -41,7 +41,7 @@
     "\n",
     "For an example, see this project's  [conf.py](conf.py) file.\n",
     "\n",
-    "Once your `conf.py` is in place, edit the file named `index.rst` and add the file names of your notebooks (with or without the `.ipynb` extension) to the [toctree](http://www.sphinx-doc.org/en/master/usage/restructuredtext/directives.html#directive-toctree) directive.\n",
+    "Once your `conf.py` is in place, edit the file named `index.rst` and add the file names of your notebooks (without the `.ipynb` extension) to the [toctree](http://www.sphinx-doc.org/en/master/usage/restructuredtext/directives.html#directive-toctree) directive.\n",
     "For an example, see this project's  [index.rst](index.rst) file."
    ]
   },
@@ -371,7 +371,7 @@
    "name": "python",
    "nbconvert_exporter": "python",
    "pygments_lexer": "ipython3",
-   "version": "3.7.1"
+   "version": "3.7.2rc1"
   }
  },
  "nbformat": 4,