Remove incorrect otherwise

You're supposed to use otherwise where you need a Boolean, not a pattern
match. This is misleadingly shadowing the real otherwise. Use _ instead.

src/ShellCheck/Data.hs

@@ -135,6 +135,6 @@ shellForExecutable name =
         "ksh"   -> return Ksh
         "ksh88" -> return Ksh
         "ksh93" -> return Ksh
-        otherwise -> Nothing
+        _ -> Nothing
 
 flagsForRead = "sreu:n:N:i:p:a:t:"