Change PROMPT_GO from "URL:" to "Go:"

This looks more apropriate because URL is too specific and _SURF_GO can
be set to other things.

config.def.h

@@ -50,7 +50,7 @@ static int winsize[] = { 800, 600 };
 static WebKitFindOptions findopts = WEBKIT_FIND_OPTIONS_CASE_INSENSITIVE |
                                     WEBKIT_FIND_OPTIONS_WRAP_AROUND;
 
-#define PROMPT_GO   "URL:"
+#define PROMPT_GO   "Go:"
 #define PROMPT_FIND "Find:"
 
 /* SETPROP(readprop, setprop, prompt)*/