restore the correct Unicode ellipsis character

It looks like this was accidentally replaced with '?' in the patch
"HsSyn clean up for indexed types".  (see bug #1294)

compiler/parser/Lexer.x

@@ -646,7 +646,7 @@ reservedSymsFM = listToUFM $
        ,("∀",	ITforall,	bit glaExtsBit)
        ,("→",   ITrarrow,	bit glaExtsBit)
        ,("←",   ITlarrow,	bit glaExtsBit)
-       ,("?", 	ITdotdot,	bit glaExtsBit)
+       ,("⋯", 	ITdotdot,	bit glaExtsBit)
         -- ToDo: ideally, → and ∷ should be "specials", so that they cannot
         -- form part of a large operator.  This would let us have a better
         -- syntax for kinds: ɑ∷*→* would be a legal kind signature. (maybe).