Added an expression method to Metric
Added an expression method to Metric

Seikitsu/gooddata-ruby,korczis/gooddata-ruby,lubosvesely/gooddata-ruby,vhtien/gooddata-ruby,korczis/gooddata-ruby,fluke777/gooddata-ruby,vhtien/gooddata-ruby,fluke777/gooddata-ruby,Seikitsu/gooddata-ruby,vhtien/gooddata-ruby,lubosvesely/gooddata-ruby,lubosvesely/gooddata-ruby,Seikitsu/gooddata-ruby,fluke777/gooddata-ruby