Stop using unsafe characters

Several characters used for short path generation are unsafe to
use without escaping. Remove those.

src/lua/util.lua

@@ -82,8 +82,8 @@ end
 local url_characters = 
 	[[abcdefghijklmnopqrstuvwxyz]]..
 	[[ABCDEFGHIJKLMNOPQRSTUVWXYZ]]..
-	[[0123456789]]..
-	[[$-+!*'(),]]
+	[[0123456789]]
+
 local url_characters_rev = {}
 for i = 1,string.len(url_characters) do
 	url_characters_rev[string.sub(url_characters,i,i)] = i