DOC: Remove Anaconda installation link

... because it has changed so many times and I'm sick of updating it.

Author: mgeier

doc/installation.ipynb

@@ -25,9 +25,8 @@
     "\n",
     "If you are using the `conda` package manager\n",
     "(e.g. with\n",
-    "[Miniforge](https://github.com/conda-forge/miniforge),\n",
-    "[Miniconda](https://docs.conda.io/en/latest/miniconda.html) or\n",
-    "[Anaconda](https://www.anaconda.com/download#downloads)),\n",
+    "[Miniforge](https://github.com/conda-forge/miniforge) or\n",
+    "[Miniconda](https://docs.conda.io/en/latest/miniconda.html)),\n",
     "you can install `nbsphinx` from the [conda-forge](https://conda-forge.org/) channel:\n",
     "\n",
     "    conda install -c conda-forge nbsphinx\n",