Fixed Twitter link for SAP UI 5

sapui5 != reactjs ;) 
Added the official openui5 account. 
Maybe this should have been two pull requests?

learn.json

@@ -1854,8 +1854,11 @@
 				"name": "API Reference",
 				"url": "https://sapui5.netweaver.ondemand.com/sdk/#content/Overview.html"
 			}, {
-				"name": "Twitter",
-				"url": "https://twitter.com/search?q=%23reactjs"
+				"name": "Twitter Search",
+				"url": "https://twitter.com/search?q=%23sapui5"
+			}, {
+				"name": "OpenUI5 Twitter", 
+				"url": "https://twitter.com/OpenUI5"
 			}]
 		}]
 	},