Update fr15-2.txt

Thanks Yugantar for the catch!  

From Discord:

```
Yugantar — Yesterday at 11:33 PM
@everyone Heads up, in the Murdock dataset, for the list length of 15 and presentation rate of 2 (file named fr15-2.txt), datapoint number 86 has a number '16' in it. Since only 15 words were shown, no one could have recalled the 16th word in the list. My guess is it is 15 and is a typo. So correct it in your code before you run it.
```

Author: jeremymanning

content/assignments/Assignment_2:Search_of_Associative_Memory_Model/Murd62 data/fr15-2.txt

@@ -83,7 +83,7 @@
 15 13 14 11 3 6 
 15 88 10 88 8 6 88 3 88 
 15 14 5 88 6 1 3 
-14 16 3 13 
+14 15 3 13 
 14 15 6 10 
 15 1 9 10 12 13 
 15 1 2 10 3 4 14