Fix typo in normalizing flow overview notebook (#178)

* Fix typo in normalizing flow overview notebook

* Update normalizing_flows_overview.ipynb

Author: emiliojorge

examples/variational_inference/normalizing_flows_overview.ipynb

@@ -71,7 +71,7 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "Formulae can be composed as a string, e.g. `'scale-loc'`, `'scale-hh*4-loc'`, `'panar*10'`. Each step is separated with `'-'`, and repeated flows are defined with `'*'` in the form of `'<flow>*<#repeats>'`.\n",
+    "Formulae can be composed as a string, e.g. `'scale-loc'`, `'scale-hh*4-loc'`, `'planar*10'`. Each step is separated with `'-'`, and repeated flows are defined with `'*'` in the form of `'<flow>*<#repeats>'`.\n",
     "\n",
     "Flow-based approximations in PyMC3 are based on the `NormalizingFlow` class, with corresponding inference classes named using the `NF` abbreviation (analogous to how `ADVI` and `SVGD` are treated in PyMC3).\n",
     "\n",