Merge pull request #236 from 7415963987456321/missing_comma

Add missing comma to the help file.

Author: haorenW1025

doc/completion-nvim.txt

@@ -221,7 +221,7 @@ g:completion_chain_complete_list	    *g:completion_chain_complete_list*
 	let g:completion_chain_complete_list = {
 	    \'default' : [
 	    \    {'complete_items': ['lsp']},
-	    \    {'complete_items': ['snippet']}
+	    \    {'complete_items': ['snippet']},
 	    \    {'mode': '<c-p>'},
 	    \    {'mode': '<c-n>'}
 	    \]