Schema conversion improvements

[jverhoeven]

Your cashay client looks great, but got stuck at step 1 when trying to introspect/minimize my schema from my Django Graphql server (and thus had no JS GraphQLSchema file).

Changes:
HTTP schema request requires application/json header (at least on some servers).
When requested over HTTP, the schema is already introspected, so only minimize.
Also allow introspected schema reading via file.

[coveralls]

Coverage remained the same at 76.305% when pulling 7cc33fe on jverhoeven:master into 1ab2e45 on mattkrick:master.

[mattkrick]

Thanks for the PR! At first glance this looks good, I've got some time to test it tomorrow night to see if it works in all cases. I'm curious how you were able to get rid of doing a require(foo).default after transpiling.

[jverhoeven]

Thanks. Regarding the require(foo).default I am afraid ignorance is bliss. I needed to just do a require without '.default' to allow already introspected JSON schemas as well. Did not run into problems myself, so let me know if this is an issue in use cases beyond my test scope.

[theobat]

Can I provide any help with tests to merge this PR ? doesn't seem like a big deal at first glance...

Thanks. Regarding the require(foo).default I am afraid ignorance is bliss. I needed to just do a require without '.default' to allow already introspected JSON schemas as well. Did not run into problems myself, so let me know if this is an issue in use cases beyond my test scope.

Perhaps we need tests in different context for the require ? I don't really see how to do that though