Log raw JSON messages/responses rather than Ruby-parsed and inspected

This allows problems to be more easily reproduced and also allows for
the logger output to be programatically parsed (by languages other than
Ruby).

lib/capybara/poltergeist/browser.rb

@@ -268,11 +268,13 @@ module Capybara::Poltergeist
     end
 
     def command(name, *args)
-      message = { 'name' => name, 'args' => args }
-      log message.inspect
+      message = JSON.dump({ 'name' => name, 'args' => args })
+      log message
 
-      json = JSON.load(server.send(JSON.dump(message)))
-      log json.inspect
+      response = server.send(message)
+      log response
+
+      json = JSON.load(response)
 
       if json['error']
         klass = ERROR_MAPPINGS[json['error']['name']] || BrowserError

spec/integration/session_spec.rb

@@ -540,7 +540,7 @@ describe Capybara::Session do
       @session.visit("/")
       @session.find(:css, "a").click
 
-      position = eval(TestSessions.logger.messages.last)["response"]["position"]
+      position = JSON.load(TestSessions.logger.messages.last)["response"]["position"]
       expect(position["x"]).to_not be_nil
       expect(position["y"]).to_not be_nil
     end

spec/unit/browser_spec.rb

@@ -11,13 +11,13 @@ module Capybara::Poltergeist
       subject      { Browser.new(server, client, logger) }
 
       it 'logs requests and responses to the client' do
-        request  = { 'name' => 'where is', 'args' => ["the love?"] }
-        response = { 'response' => '<3' }
-        server.stub(:send).with(MultiJson.dump(request)).and_return(JSON.dump(response))
+        request = %({"name":"where is","args":["the love?"]})
+        response = %({"response":"<3"})
+        server.stub(:send).with(request).and_return(response)
 
         subject.command('where is', 'the love?')
 
-        expect(logger.string).to eq("#{request.inspect}\n#{response.inspect}\n")
+        expect(logger.string).to eq("#{request}\n#{response}\n")
       end
     end
   end