fix(mbake): format using stdin (#798)

* fix(mbake): correct mbake command and use stdin

* fix(mbake): correct formatting

* fix(bake): merge changes into existing bake formatter

Author: Saul-CD

lua/conform/formatters/bake.lua

@@ -5,6 +5,5 @@ return {
     description = "A Makefile formatter and linter.",
   },
   command = "mbake",
-  args = { "format", "$FILENAME" },
-  stdin = false,
+  args = { "format", "--stdin" },
 }