Fix typo in notebook-covidspread

2-Working-With-Data/07-python/notebook-covidspread.ipynb

@@ -1793,7 +1793,7 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "Now let's compute the number of new infected people each day. This will allow us to see the speed at which pandemic progresses. The easiest day to do it is to use `diff`:"
+    "Now let's compute the number of new infected people each day. This will allow us to see the speed at which pandemic progresses. The easiest way to do it is to use `diff`:"
    ]
   },
   {