Fix last4Digits assignment to use string conversion

Convert cardNumber to string before slicing to get last 4 digits.

Author: mrafeie

Sprint-2/2-mandatory-errors/3.js

@@ -1,9 +1,11 @@
 const cardNumber = 4533787178994213;
-const last4Digits = cardNumber.slice(-4);
+const last4Digits = String(cardNumber).slice(-4);
 
 // The last4Digits variable should store the last 4 digits of cardNumber
 // However, the code isn't working
 // Before running the code, make and explain a prediction about why the code won't work
 // Then run the code and see what error it gives.
 // Consider: Why does it give this error? Is this what I predicted? If not, what's different?
 // Then try updating the expression last4Digits is assigned to, in order to get the correct value
+
+// The .slice() method works on strings, but numbers don't have a .slice() method