Replace spammy radon image with Wikimedia version (#4195)

* Updated Mauna Loa notebook

* Replaced bad radon image link

* Added newline

Author: fonnesbeck

docs/source/notebooks/GLM-hierarchical.ipynb

@@ -36,7 +36,7 @@
     "Gelman et al.'s (2007) radon dataset is a classic for hierarchical modeling. In this dataset the amount of the radioactive gas radon has been measured among different households in all counties of several states. Radon gas is known to be the highest cause of lung cancer in non-smokers. It is believed to be more strongly present in households containing a basement and to differ in amount present among types of soil.\n",
     "Here we'll investigate this differences and try to make predictions of radonlevels in different counties based on the county itself and the presence of a basement. In this example we'll look at Minnesota, a state that contains 85 counties in which different measurements are taken, ranging from 2 to 116 measurements per county. \n",
     "\n",
-    "![radon](http://www.fix-your-radon.com/images/how_radon_enters.jpg)"
+    "![radon](https://upload.wikimedia.org/wikipedia/commons/b/b9/CNX_Chem_21_06_RadonExpos.png)"
    ]
   },
   {