Merge pull request #97 from gperdrizet/dev

Added Lesson 13 demo dataset and updated notebook to load data direct…

Author: gperdrizet

data/datasets.yml

@@ -33,4 +33,11 @@ units:
           - name: "Synthetic fitness and biometric data"
             file: "fitness.csv"
           - name: "Synthetic meteorology data"
-            file: "weather.csv"
+            file: "weather.csv"
+
+      - number: "13"
+        title: "Probability distributions"
+        assignment: "Lesson 12 activity"
+        datasets:
+          - name: "Synthetic online sales data"
+            file: "online_sales.csv"