fix: flow: prevent RequestOptions null error

[KROT47]

Trying to do so:

createNetworkInterface( {
        uri: '/api/v1/graphql',
        opts: {
            // Additional fetch options like `credentials` or `headers`
            credentials: 'same-origin',
        }
} )

will lead to flow error:

node_modules/apollo-client/apollo.umd.js.flow:124
    124:   opts?: ?RequestOptions,
                  ^^^^^^^^^^^^^^^ null. This type is incompatible with the expected param type of
                       v
     38:         opts: {
     39:             // Additional fetch options like `credentials` or `headers`
     40:             credentials: 'same-origin',
     41:         }
                 ^ object literal. See: config/project/index.js:38

because NetworkInterfaceOptions and BatchingNetworkInterfaceOptions were defined as interfaces not types.

[apollo-cla]

@KROT47: Thank you for submitting a pull request! Before we can merge it, you'll need to sign the Meteor Contributor Agreement here: https://contribute.meteor.com/

[apollo-cla]

	Messages
📖	Please add your name and email to the AUTHORS file (optional)
📖	If this was a change that affects the external API, please update the docs and post a link to the PR in the discussion

Generated by 🚫 dangerJS

[jbaxleyiii]

@KROT47 can you add a test for this in the /test/flow.js file?

[jbaxleyiii]

Thanks!