Address nightly build failure (ProjectPythia#618)

* Update environment.yml

* add header targets

* jupyterbook link fails jupyterbooks link checking :P

* Update environment.yml

* 3 links

Author: jukent

core/matplotlib/histograms-piecharts-animation.ipynb

@@ -231,7 +231,7 @@
    "id": "c516ce4b",
    "metadata": {},
    "source": [
-    "(animations)=\n",
+    "(animations)= \n",
     "## Animations"
    ]
   },