feat(loader): Use relative path inside SDL

Use the file path instead of file content to import schema. Set Jest's environment to node
to avoid the error with jsdom's localStorage, see jestjs/jest#6766 and jsdom/jsdom#2304.

BREAKING CHANGE: Use absolute path inside DSL won't work anymore, but now will be the same
behavior of `graphql-import` dealing with paths.

Fix prisma-labs#10

jest.config.js

@@ -10,5 +10,6 @@ module.exports = {
     "js",
     "ts",
     "node"
-  ]
+  ],
+  "testEnvironment": "node"
 }

src/index.ts

@@ -2,8 +2,11 @@ import { importSchema } from 'graphql-import'
 
 export default function(source) {
   const callback = this.async();
+  const isFileRegex = /\.graphql$/i
 
   this.cacheable()
 
-  callback(null, `module.exports = \`${importSchema(source).replace(/`/g, '\\`')}\``)
+  const sdl = importSchema(isFileRegex.test(this.resource) ? this.resource : source)
+
+  callback(null, `module.exports = \`${sdl.replace(/`/g, '\\`')}\``)
 }

test/fixtures/complex.graphql

@@ -1,6 +1,6 @@
-# import { A } from 'test/fixtures/a.graphql'
-# import { B } from 'test/fixtures/b.graphql'
-# import { C D } from 'test/fixtures/cd.graphql'
+# import { A } from './a.graphql'
+# import { B } from './b.graphql'
+# import { C D } from './cd.graphql'
 
 type Complex  {
   id: ID!