refactor retrieving ICS file

lib/services/ics-generator.js

@@ -0,0 +1,16 @@
+const ics = require('ics')
+
+const generateICS = async(data) => {
+  return new Promise((resolve, reject) => {
+    ics.createEvent(data, (err, value) => {
+      if (err) {
+        reject(err)
+        return
+      }
+
+      resolve(value)
+    })
+  })
+}
+
+module.exports = generateICS