Fix function argument (#1002)

Fixes #1000

Author: mattn

autoload/lsp/internal/diagnostics/under_cursor.vim

@@ -3,7 +3,7 @@
 " options = {
 "   'server': '',        " optional
 " }
-function! lsp#internal#diagnostics#under_cursor#get_diagnostic() abort
+function! lsp#internal#diagnostics#under_cursor#get_diagnostic(...) abort
     let l:options = get(a:000, 0, {})
     let l:server = get(l:options, 'server', '')
     let l:bufnr = bufnr('%')

autoload/lsp/ui/vim/code_action.vim

@@ -39,7 +39,7 @@ function! lsp#ui#vim#code_action#do(option) abort
     let l:bufnr = bufnr('%')
     let l:command_id = lsp#_new_command()
     for l:server_name in l:server_names
-        let l:diagnostic = lsp#internal#diagnostics#under_cursor#get_diagnostic(l:server_name)
+        let l:diagnostic = lsp#internal#diagnostics#under_cursor#get_diagnostic({'server': l:server_name})
         call lsp#send_request(l:server_name, {
                     \ 'method': 'textDocument/codeAction',
                     \ 'params': {