fix module dependencies

Author: ldeniau

src/madl_json.lua

@@ -386,10 +386,8 @@ end
 
 -- MAD extensions --------------------------------------------------------------
 
-local openfile in MAD.utility
-
 function json.write (filnam_, val)
-  local file = assert(openfile(filnam_, 'w'),
+  local file = assert(MAD.utility.openfile(filnam_, 'w'),
                       "unable to open JSON file in write mode")
   file:write(json.encode(val))
   if is_string(filnam_) then file:close() else file:flush() end
@@ -400,7 +398,7 @@ function json.print (val)
 end
 
 function json.read (filnam_)
-  local file = assert(openfile(filnam_, 'r'),
+  local file = assert(MAD.utility.openfile(filnam_, 'r'),
                       "unable to open JSON file in read mode")
   local val = json.decode(file:read("*a"))
   if is_string(filnam_) then file:close() end