code update and add cache

Author: sheetalkharab

Sprint-2/improve_with_caches/fibonacci/fibonacci.py

@@ -1,4 +1,11 @@
+cache = {}
+
 def fibonacci(n):
+    if(n) in cache:
+        return cache[n]
     if n <= 1:
         return n
-    return fibonacci(n - 1) + fibonacci(n - 2)
+    
+    result = fibonacci(n - 1) + fibonacci(n - 2)
+    cache[n] = result 
+    return result