feat(numpy): update exercise 8

- update delemiter in formula to import dataset
- update subject request to make it consistent with audit

subjects/ai/numpy/README.md

@@ -217,7 +217,7 @@ How to tell if a given 2D array has null columns?
 
 4. What is the average % of alcohol on all wines in the data set ? If needed, drop `np.nan` values
 
-5. Compute the minimum, the maximum, the 25th percentile, the 50th percentile, the 75th percentile, the median (50th percentile) of the pH
+5. Compute the minimum, the maximum, the 25th percentile, the 50th percentile, the 75th percentile, the mean of the pH
 
 6. Compute the average quality of the wines having the 20% least sulphates
 

subjects/ai/numpy/audit/README.md

@@ -244,7 +244,7 @@ There are two steps in this exercise:
 
 ##### The exercise is validated if all questions of the exercise are validated
 
-###### Has the text file successfully been loaded in a NumPy array with `genfromtxt('winequality-red.csv', delimiter=',')` and the reduced arrays weights **76800 bytes**?
+###### Has the text file successfully been loaded in a NumPy array with `genfromtxt('winequality-red.csv', delimiter=';')` and the reduced arrays weights **76800 bytes**?
 
 ###### Is the output the following?