[Meltdown Mitigation]: Correct Typo in introduction.md (#3758)

great --> greater on line 53.

Author: BethanyG

exercises/concept/meltdown-mitigation/.docs/introduction.md

@@ -50,7 +50,7 @@ elif y > z:
 else:
     print("z is greater than x and y")
 ...
->>> z is great than x and y
+>>> z is greater than x and y
 ```
 
 [Boolean operations][boolean operations] and [comparisons][comparisons] can be combined with conditionals for more complex testing: