Update field resolver interface to allow typed args

[luk3thomas]

Related to #704

This change allows me to specify a type for the args object of a resolver. Without this change I cannot specify types for the args object of a resolver. As an example

const resolvers = {
  Query: {
    hello: (_parent: object, args: { id: string }) => `Hello ${args.id}!`,
  },
};

☝️ Does not compile.

[ts]
Argument of type '{ typeDefs: DocumentNode; resolvers: { Query: { hello: (_parent: object, args: { id: string; }) => string; }; }; }' is not assignable to parameter of type 'Config'.
  Types of property 'resolvers' are incompatible.
    Type '{ Query: { hello: (_parent: object, args: { id: string; }) => string; }; }' is not assignable to type 'IResolvers<any, any>'.
      Property 'Query' is incompatible with index signature.
        Type '{ hello: (_parent: object, args: { id: string; }) => string; }' is not assignable to type '(() => any) | GraphQLScalarType | IEnumResolver | IResolverObject<any, any> | IResolverOptions<any, any>'.
          Type '{ hello: (_parent: object, args: { id: string; }) => string; }' has no properties in common with type 'IResolverOptions<any, any>'.
(property) typeDefs: DocumentNode

TODO:

• If this PR is a new feature, reference an issue where a consensus about the design was reached (not necessary for small changes)
• Make sure all of the significant new logic is covered by tests
• Rebase your changes on master so that they can be merged easily
• Make sure all tests and linter rules pass
• Update CHANGELOG.md with your change. Include a description of your change, link to PR (always) and issue (if applicable). Add your CHANGELOG entry under vNEXT. Do not create a new version number for your change yourself.

[apollo-cla]

@luk3thomas: 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/

[hwillson]

Thanks @luk3thomas - LGTM!

[booooh]

Maybe I'm doing something wrong, but I bumped my version of apollo-server-express to 2.2.0-alpha, which seems to take in this change, and I'm still seeing the same issue.

src/index.ts:21:3 - error TS2322: Type '{ Query: { hello: (parent: any, args: { name: string; }) => string; }; }' is not assignable to type 'IResolvers<any, any>'.
  Property 'Query' is incompatible with index signature.
    Type '{ hello: (parent: any, args: { name: string; }) => string; }' is not assignable to type 'GraphQLScalarType | IEnumResolver | (() => any) | IResolverObject<any, any> | IResolverOptions<any, any>'.
      Type '{ hello: (parent: any, args: { name: string; }) => string; }' has no properties in common with type 'IResolverOptions<any, any>'.

[booooh]

Specifically, the following 2 examples demonstrate the failure vs a working example. Note that the args needs to be typed as a Mapping in order for this to work

const good: IFieldResolver<any, any> = (p: any, args: { [key: string]: any }) => `hello ${args.id}!`; //Works :)
const bad: IFieldResolver<any, any> = (p: any, args: { id: string }) => `hello ${args.id}!`; //Error :(