Fix error when call UltestSummaryOpen

[ktakayama]

Error detected while processing function dein#autoload#_on_cmd:
line   13:
E118: Too many arguments for function: ultest#summary#open

This problem occurs from #67

current code

vim-ultest/plugin/ultest.vim

Line 342 in dfea06d

command! -bang UltestSummaryOpen call ultest#summary#open(expand("<bang>") == "!")

vim-ultest/autoload/ultest/summary.vim

Lines 36 to 40 in dfea06d

	function! ultest#summary#open() abort
	if !s:IsOpen()
	call s:OpenNewWindow()
	endif
	endfunction

[rcarriga]

Thanks for the PR! 😄