Avoid useless space in default empty argument string

Author: alerque

plugin/vimux.vim

@@ -71,7 +71,7 @@ function! VimuxOpenRunner()
   if _VimuxOption("g:VimuxUseNearest", 1) == 1 && nearestIndex != -1
     let g:VimuxRunnerIndex = nearestIndex
   else
-    let extraArguments = _VimuxOption("g:VimuxOpenExtraArgs", " ")
+    let extraArguments = _VimuxOption("g:VimuxOpenExtraArgs", "")
     if _VimuxRunnerType() == "pane"
       let height = _VimuxOption("g:VimuxHeight", 20)
       let orientation = _VimuxOption("g:VimuxOrientation", "v")