refactor: remove context.done and replace with object return

Continues work started in probot#18

Author: Matthew Cantelon

index.js

@@ -65,10 +65,10 @@ module.exports.serverless = appFn => {
 
     // Bail for null body
     if (!event.body) {
-      return context.done(null, {
+      return {
         statusCode: 400,
         body: 'Event body is null.'
-      })
+      }
     }
 
     // Do the thing

tests/index.test.js

@@ -49,10 +49,8 @@ describe('serverless-lambda', () => {
       }
     }
 
-    await handler(event, context)
-    expect(context.done).toHaveBeenCalledWith(null, expect.objectContaining({
-      statusCode: 400
-    }))
+    const result = await handler(event, context)
+    expect(result.statusCode).toBe(400)
     expect(spy).not.toHaveBeenCalled()
   })