migrate to new optparse

adiff.cabal

@@ -52,7 +52,7 @@ executable adiff
   build-depends: base ^>=4.13.0.0,
                  mmap ^>=0.5,
                  regex-tdfa ^>= 1.3,
-                 optparse-applicative ^>=0.15,
+                 optparse-applicative ^>=0.16,
                  bytestring ^>= 0.10.12,
                  vector ^>=0.12,
 		 utf8-string ^>=1.0

src/Version.hs

@@ -18,5 +18,5 @@ versionOption prog =
 helperOption :: Parser (a -> a)
 helperOption =
   abortOption
-    ShowHelpText
+    (ShowHelpText Nothing)
     (long "help" <> short 'h' <> help "Show this help text")