Feature/apollo header support

[mwarger]

Fixes #151

Adds support for --header flag to CLI. Example:

mst-gql --header=X-Hasura-Admin-Secret:supersecret

Adds support for a header in a config object. Example (in config or package.json):

"mst-gql": {
    "input": "http://localhost:8080/v1/graphql",
    "format": "ts",
    "outDir": "src/models",
    "roots": [
      "todos",
      "otherthings"
    ],
    "header": {
      "x-hasura-admin-secret": "supersecret",
    }
  }

Feedback is welcome.

[chrisdrackett]

looks good to me, I just found one issue. Thanks for fixing some typos as well :)

[mwarger]

@chrisdrackett - any thoughts on this?

[chrisdrackett]

Make sure the tests and examples run,

Just did a quick test running example 1 and it fails with ReferenceError: defaultConfig is not defined.

[barbalex]

The second this is published I will start my new project 🚀

[barbalex]

Works like a charm. You guys are heroes!