vim:keys: Add mapping for commit amending

Map `<leader>gca` to fugitives `G commit --amend`, as I use that quite
often.

Also change the normal commit mapping to use double `c`s for unambiguity
between the mappings and as I already got the habit of pressing `c`
twice to skip waiting `timeoutlen` (As the mapping was already
ambiguous with `<leader>gcd` for `:Gcd`).

.config/vim/vimrc.d/40-keys.vim

@@ -119,8 +119,10 @@ nmap <leader>gu :!git checkout -- %<CR>
 if exists('g:loaded_fugitive')
 	" Interactive `git status`
 	nmap <leader>gg :G<CR>
-	" Using fugitive.vim, start a commit and open the message in a new split
-	nmap <leader>gc :G commit<CR>
+	" Start a commit and open the message in a split
+	nmap <leader>gcc :G commit<CR>
+	" Amend the current commit and open the message in a split
+	nmap <leader>gca :G commit --amend<CR>
 	" Move to root of directory
 	nmap <leader>gcd :Gcd<CR>
 	" git blame in scroll bound vertical split (only the commit hashes, see