Fix a typo

Author: Janiczek

src/Test/Runner.elm

@@ -485,7 +485,7 @@ type Simplifiable a
 {-| Given a fuzzer, return a random generator to produce a value and a
 Simplifiable. The value is what a fuzz test would have received as input.
 
-Note that fuzzers aren't generated to succeed, which is why this function returns
+Note that fuzzers aren't guaranteed to succeed, which is why this function returns
 a Result. The String inside the Err case will contain a failure reason.
 
 -}