Get rid of a few Ruby warnings

Fixes issue 8027
Fixes issue 8028

Author: jarib

rb/lib/selenium/webdriver/remote/bridge.rb

@@ -66,6 +66,8 @@ def initialize(opts = {})
 
           @http          = http_client
           @capabilities  = create_session(desired_capabilities)
+
+          @file_detector = nil
         end
 
         def browser

rb/lib/selenium/webdriver/remote/http/default.rb

@@ -119,7 +119,7 @@ def use_proxy?
                 host == server_url.host || (
                   begin
                     IPAddr.new(host).include?(server_url.host)
-                  rescue ArgumentError => ex
+                  rescue ArgumentError
                     false
                   end
                 )