Change $FILEPATH to $FILENAME in the fourmolu configuration. (#1601)

Co-authored-by: disco-dave <[email protected]>

Author: Disco-Dave

doc/BUILTINS.md

@@ -3253,7 +3253,7 @@ local sources = { null_ls.builtins.formatting.fourmolu }
 - Filetypes: `{ "haskell" }`
 - Method: `formatting`
 - Command: `fourmolu`
-- Args: `{ "--stdin-input-file", "$FILEPATH" }`
+- Args: `{ "--stdin-input-file", "$FILENAME" }`
 
 ### [fprettify](https://github.com/pseewald/fprettify)
 

lua/null-ls/builtins/formatting/fourmolu.lua

@@ -13,7 +13,7 @@ return h.make_builtin({
     filetypes = { "haskell" },
     generator_opts = {
         command = "fourmolu",
-        args = { "--stdin-input-file", "$FILEPATH" },
+        args = { "--stdin-input-file", "$FILENAME" },
         to_stdin = true,
     },
     factory = h.formatter_factory,