Fix NetworkMiddleware flow type

[META-DREAMER]

When adding middleware and afterware to the network interface, it should only accept either applyMiddleware or applyBatchMiddleware, but not both. The way to types were defined, it would accept both types of middleware. This is the error that the test case I added would give:

test/flow.js:33
 33: const middleware: MiddlewareInterface[] = [{
                       ^^^^^^^^^^^^^^^^^^^ property `applyMiddleware` of MiddlewareInterface. Property not found in
 97: export type NetworkMiddleware = Array<MiddlewareInterface | BatchMiddlewareInterface>;
                                                                 ^^^^^^^^^^^^^^^^^^^^^^^^ BatchMiddlewareInterface. See: src/index.js.flow:97

test/flow.js:48
 48: const afterware: AfterwareInterface[] = [{
                      ^^^^^^^^^^^^^^^^^^ property `applyAfterware` of AfterwareInterface. Property not found in
 98: export type NetworkAfterware = Array<AfterwareInterface | BatchAfterwareInterface>;
                                                               ^^^^^^^^^^^^^^^^^^^^^^^ BatchAfterwareInterface. See: src/index.js.flow:98

[mention-bot]

@HammadJ, thanks for your PR! By analyzing the history of the files in this pull request, we identified @michalkvasnicak, @kamilkisiela and @tgriesser to be potential reviewers.

[apollo-cla]

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[jbaxleyiii]

@HammadJ thank you for this! 👍 for improving flow types!