Avoid overriding package.json

Resolves #45.

jest-preset.coffee

@@ -1,17 +1,8 @@
 import fs from 'fs'
 import path from 'path'
 import {compile, helpers as h, FILE_EXTENSIONS} from 'coffeescript'
-import package_json, {jest} from './package'#.json
 
-{name} = path.parse __filename
 coffee = FILE_EXTENSIONS.map (ext) => ext[1..]
-glob = "*.@(#{coffee.join '|'})"
-
-package_json.main = jest.preset = "./#{name}"
-[staged] = Object.values package_json['lint-staged']
-package_json['lint-staged'] = [glob]: staged
-delete jest.rootDir
-fs.writeFileSync 'package.json', JSON.stringify package_json, null, 2
 
 if describe?
   override = describe
@@ -20,7 +11,7 @@ if describe?
 
 module.exports =
   moduleFileExtensions: ['js', 'json', coffee...]
-  testMatch: ["<rootDir>/*@(test|spec)?(s){/**/,}#{glob}"]
+  testMatch: ["<rootDir>/*@(test|spec)?(s){/**/,}@(#{coffee.join '|'})"]
   testPathIgnorePatterns: ['node_modules', 'fixtures']
   transform: [coffee.join '|']: __filename
   setupFilesAfterEnv: [__filename ]