Added the modern pages and removed the "Developer" tenants (SharePoint#1255)

Added the modern pages and removed the "Developer" tenants

Author: PiotrekKrakowiak

docs/spfx/web-parts/overview-client-side-web-parts.md

@@ -10,7 +10,7 @@ ms.prod: sharepoint
 
 SharePoint client-side web parts are controls that appear inside a SharePoint page but run locally in the browser. They're the building blocks of pages that appear on a SharePoint site. 
 
-You can build client-side web parts using modern script development tools and the SharePoint workbench (a development test surface), and you can deploy your client-side web parts to classic web part pages in Office 365 Developer tenants.  
+You can build client-side web parts using modern script development tools and the SharePoint workbench (a development test surface), and you can deploy your client-side web parts to modern pages and classic web part pages in Office 365 tenants.  
 
 In addition to plain JavaScript projects, you can build web parts alongside common scripting frameworks, such as AngularJS and React. For example, you can use React along with components from Office UI Fabric React to quickly create experiences based on the same components used in Office 365.