title: Apollo-server-express returning "cannot Get /" instead of the Graphql playground
body: <p>so I have this code for both my server.js and schema.js from following the apollo doc tutorial <a href="https://www.apollographql.com/docs/tutorial/introduction/" rel="nofollow noreferrer">https://www.apollographql.com/docs/tutorial/introduction/</a></p>
  <p>server.js</p>
  <pre><code>import apollo from &quot;apollo-server-express&quot;;
  const { ApolloServer } = apollo;
  import express from &quot;express&quot;;
  import typeDefs from &quot;./schema.js&quot;;
  
  const app = express();
  const server = new ApolloServer({
    typeDefs,
    playground: true,
  });
  
  server.applyMiddleware({ app });
  
  const PORT = process.env.PORT || 4000;
  app.listen(PORT, () =&gt; {
    console.log(`operating on port ${PORT}`);
  })
  </code></pre>
  <p>schema.js</p>
  <pre><code>import pkg from &quot;apollo-server-express&quot;
  const { gql } = pkg
  
  // defining schema
   const typeDefs = gql`
    type Launch {
      id: ID!
      site: String
      mission: Mission
      rocket: Rocket
      isBooked: Boolean!
    }
    type Rocket {
      id: ID!
      name: String
      type: String
    }
  
    type User {
      id: ID!
      email: String!
      trips: [Launch]!
    }
  
    type Mission {
      name: String
      missionPatch(size: PatchSize): String
    }
  
    enum PatchSize {
      SMALL
      LARGE
    }
    type Query {
      launches: [Launch]!
      launch(id: ID!): Launch
      me: User
    }
    type Mutation {
      bookTrips(launchIds: [ID]!): TripUpdateResponse!
      cancelTrip(launchId: ID!): TripUpdateResponse!
      login(email: String): String # login token
    }
    type TripUpdateResponse {
      success: Boolean!
      message: String
      launches: [Launch]
    }
  `
  export default typeDefs
  </code></pre>
  <hr />
  <p>only tweak I did was to choose the ES modules method of import/exporting modules over the commonJS way as used in the documentation, which I think shouldn't be a problem, it compiles without errors but instead of getting the graphql playground to see my schema, I get a <code>cannot Get /</code></p>
  <p>I haven't done the resolvers, but at this point, I believe I should see the playground in action already. as per the docs</p>