feat(ft): support for block comments in coq (#465)

Block comments are legal in Coq, with the same syntax as line comments
`(*%s*)`. This syntax comes from OCaml, for which block comments are
indeed already specified.

Co-authored-by: Loïc <lpeyrot@irif.fr>

Author: lowyck

lua/Comment/ft.lua

@@ -51,7 +51,7 @@ local L = setmetatable({
     cmake = { M.hash, M.hash_bracket },
     conf = { M.hash },
     conkyrc = { M.dash, M.dash_bracket },
-    coq = { M.fsharp_b },
+    coq = { M.fsharp_b, M.fsharp_b },
     cpp = { M.cxx_l, M.cxx_b },
     cs = { M.cxx_l, M.cxx_b },
     css = { M.cxx_b, M.cxx_b },