feat(Neovim): Correct defaults for restore-cursor

When restoring the cursor to last file's position, there was an
inconsistency between Neovim and Vim for commit files.  That was because
Neovim's defaults didn't properly detect the filetype in such cases.
The current patch corrects that with a recipe copied from Neovim's help
docs.

nvim/defaults.vim

@@ -1,15 +1,19 @@
-" Some settings Vim has on its defaults.vim that NeoVim hasn't set by default
+" Some settings Vim has on “defaults.vim” that Neovim hasn't set by default
 
 set scrolloff=5
 
 if has('mouse')
-	set mouse=a
+  set mouse=a
 endif
 
-augroup vimStartup
-	au!
-	autocmd BufReadPost *
-		\ if line("'\"") >= 1 && line("'\"") <= line("$") && &ft !~# 'commit'
-		\ |   exe "normal! g`\""
-		\ | endif
+augroup RestoreCursor
+  autocmd!
+  " This is slightly different than Vim's defaults.vim, but taken from
+  " “:h restore-cursor” for Neovim
+  autocmd BufRead * autocmd FileType <buffer> ++once
+    \ let s:line = line("'\"")
+    \ | if s:line >= 1 && s:line <= line("$") && &filetype !~# 'commit'
+    \      && index(['xxd', 'gitrebase'], &filetype) == -1
+    \ |   execute "normal! g`\""
+    \ | endif
 augroup END

nvim/init.vim

@@ -32,7 +32,6 @@ if has('autocmd')
 		autocmd!
 		autocmd FileType gitcommit setlocal spell nonumber norelativenumber
 		autocmd FileType gitcommit startinsert
-		autocmd FileType gitcommit exe "normal! gg"
 	augroup END
 endif