change incorrect variable name

solution and problem statement have the calls stored in `calls`, not `log`

Author: zvory

1-js/06-advanced-functions/09-call-apply-decorators/01-spy-decorator/solution.md

@@ -1 +1 @@
-Here we can use `log.push(args)` to store all arguments in the log and `f.apply(this, args)` to forward the call.
+Here we can use `calls.push(args)` to store all arguments in the log and `f.apply(this, args)` to forward the call.