fix: visual mode contrast

For some unknown reason, the `Visual` highlight group has had pretty
poor constrast for a long time. I'm honestly not sure how it went
unnoticed for so long. Thanks to echasnovski for pointing it out on #81

lua/cyberdream/theme.lua

@@ -107,8 +107,8 @@ function M.setup()
         WinBar = { fg = t.grey, bg = t.bg },
         WinBarNC = { fg = t.grey, bg = t.bg },
         Title = { fg = t.fg },
-        Visual = { fg = t.bg, bg = t.bgHighlight },
-        VisualNOS = { fg = t.bg, bg = t.bgHighlight },
+        Visual = { bg = t.bgHighlight },
+        VisualNOS = { bg = t.bgHighlight },
         WarningMsg = { fg = t.orange },
         Whitespace = { fg = t.grey },
         WildMenu = { fg = t.bg, bg = t.blue },