Improve listchars and rendered whitespace

Make NonText blue and Whitespace foreground gray so that it looks a bit
more like in VS Code Dark+ color theme.

Closes LunarVim#1

lua/darkplus/highlights.lua

@@ -18,7 +18,7 @@ local highlights = {
 		FoldColumn = {fg = C.accent, bg = C.alt_bg, },
 		LineNr = {fg = C.gray, },
 		FloatBoder = {fg = C.gray, bg = C.alt_bg, },
-		Whitespace = {fg = C.bg, },
+		Whitespace = {fg = C.gray, },
 		VertSplit = {fg = C.bg, bg = C.gray, },
 		CursorLine = {bg = C.dark, },
 		CursorColumn = {bg = C.dark, },
@@ -53,7 +53,7 @@ local highlights = {
 		MoreMsg = {fg = C.orange, },
 		Question = {fg = C.orange, },
 		EndOfBuffer = {fg = C.bg, },
-		NonText = {fg = C.bg, },
+		NonText = {fg = C.blue, style = "bold", },
 		Variable = {fg = C.light_blue, },
 		String = {fg = C.orange, },
 		Character = {fg = C.orange, },