console.lua: use the same opacity for menu as for everything else

There was a mistake of using hex (50) instead of decimal (80) it is
converted to %x later on.

DOCS/man/console.rst

@@ -167,7 +167,7 @@ Configurable Options
     Set the font border size used for the REPL and the console.
 
 ``background_alpha``
-    Default: 20
+    Default: 80
 
     The transparency of the menu's background. Ranges from 0 (opaque) to 255
     (fully transparent).

player/lua/console.lua

@@ -32,7 +32,7 @@ local opts = {
     font = "",
     font_size = 24,
     border_size = 1.65,
-    background_alpha = 50,
+    background_alpha = 80,
     padding = 10,
     menu_outline_size = 0,
     menu_outline_color = '#FFFFFF',