Merge pull request #2278 from filakhtov/ch06-02-fix

Add the missing word to the sentence (ch06-2)

src/ch06-02-match.md

@@ -181,7 +181,7 @@ pattern we forgot! Matches in Rust are *exhaustive*: we must exhaust every last
 possibility in order for the code to be valid. Especially in the case of
 `Option<T>`, when Rust prevents us from forgetting to explicitly handle the
 `None` case, it protects us from assuming that we have a value when we might
-have null, thus making the billion-dollar mistake discussed earlier.
+have null, thus making the billion-dollar mistake discussed earlier impossible.
 
 ### The `_` Placeholder