Bump representable dependency to 3.0 (#532)

Also fixes a breaking change introduced between `representable` 2.3 and
3.0. Specifically, `:skip_undefined` is now be passed via the
`:user_options` option.

lib/google/apis/core/api_command.rb

@@ -55,7 +55,7 @@ module Google
           query[FIELDS_PARAM] = normalize_fields_param(query[FIELDS_PARAM]) if query.key?(FIELDS_PARAM)
           if request_representation && request_object
             header[:content_type] ||= JSON_CONTENT_TYPE
-            self.body = request_representation.new(request_object).to_json(skip_undefined: true)
+            self.body = request_representation.new(request_object).to_json(user_options: { skip_undefined: true })
           end
           super
         end

lib/google/apis/core/json_representation.rb

@@ -55,7 +55,7 @@ module Google
           def if_fn(name)
             ivar_name = "@#{name}".to_sym
             lambda do |opts|
-              if opts[:skip_undefined]
+              if opts[:options][:user_options] and opts[:options][:user_options][:skip_undefined]
                 if respond_to?(:key?)
                   self.key?(name) || instance_variable_defined?(ivar_name)
                 else
@@ -137,7 +137,7 @@ module Google
 
         def to_json
           representation = self.class.const_get(:Representation)
-          representation.new(self).to_json(skip_undefined: true)
+          representation.new(self).to_json(user_options: { skip_undefined: true })
         end
       end
     end