Fix typo

src/exercise.rs

@@ -235,7 +235,7 @@ path = "{}.rs""#,
 
     // Check that the exercise looks to be solved using self.state()
     // This is not the best way to check since
-    // the user can just remove the "I AM NOT DONE" string fromm the file
+    // the user can just remove the "I AM NOT DONE" string from the file
     // without actually having solved anything.
     // The only other way to truly check this would to compile and run
     // the exercise; which would be both costly and counterintuitive