Fix proxy unit tests after 7e69b3d

Author: p0deje

rb/spec/unit/selenium/webdriver/remote/capabilities_spec.rb

@@ -61,7 +61,7 @@ module Remote
         end
 
         it 'should default to no proxy' do
-          expect { Capabilities.new.proxy }.to raise_error(KeyError)
+          expect(Capabilities.new.proxy).to be_nil
         end
 
         it 'can set and get standard capabilities' do