.editorconfig: add compilers/elm/registry.dat

.editorconfig

···
 [pkgs/applications/editors/emacs-modes/recipes-archive-melpa.json]
 indent_size = unset
 
-[pkgs/build-support/dotnetenv/Wrapper/**.*]
+[pkgs/build-support/dotnetenv/Wrapper/**]
 end_of_line = unset
 insert_final_newline = unset
 trim_trailing_whitespace = unset
+
+[pkgs/development/compilers/elm/registry.dat]
+end_of_line = unset
+insert_final_newline = unset
 
 [pkgs/development/lisp-modules/quicklisp-to-nix.nix]
 indent_size = unset