Need to set modifiable for reloading commit content (#255)

plug.vim

@@ -1901,7 +1901,7 @@ function! s:preview_commit()
 
   execute 'pedit' sha
   wincmd P
-  setlocal filetype=git buftype=nofile nobuflisted
+  setlocal filetype=git buftype=nofile nobuflisted modifiable
   execute 'silent read !cd' s:shellesc(g:plugs[name].dir) '&& git show --pretty=medium' sha
   normal! gg"_dd
   setlocal nomodifiable