Switch to separate config import

Import default config from separate path (require('tailwindcss/defaultConfig')) to allow importing the default config without importing all of Tailwind, which causes errors with Webpack due to a dynamic require.

Author: reinink

.eslintignore

@@ -1,3 +1,3 @@
 /lib
 /docs
-defaultConfig.js
+defaultConfig.stub.js

__tests__/importsConfig.test.js

@@ -3,5 +3,5 @@ import config from '../defaultConfig.js'
 
 test('it can accept a config file', () => {
   tailwind('./defaultConfig.js')
-  expect(tailwind.defaultConfig()).toEqual(config)
+  expect(require('../defaultConfig.stub.js')).toEqual(config())
 })