title: Error: Error: the "filename" option is required to use includes and extends with "relative" paths
body: <p>I'm using Vue with webpack template and I'm trying to run tests with Jest. I'm also using Pug to render the templates. </p>
  
  <p>But when I run the tests I get the error:</p>
  
  <pre><code>[vue-jest] Error: Error: the "filename" option is required to use includes and extends with "relative" paths
      at undefined line 2
  
  
    at error (node_modules/vue-jest/lib/throw-error.js:2:9)
    at module.exports (node_modules/vue-jest/lib/compilers/pug-compiler.js:11:5)
    at getTemplateContent (node_modules/vue-jest/lib/template-compiler.js:11:12)
    at compileTemplate (node_modules/vue-jest/lib/template-compiler.js:23:25)
    at Object.module.exports [as process] (node_modules/vue-jest/lib/process.js:70:29)
  </code></pre>
  
  <p>Running coverage on untested files...Failed to collect coverage from /Users/magno.sousa/Documents/playground/vue-test/vuetest/src/components/HelloWorld.vue
  ERROR:
  [vue-jest] Error: Error: the "filename" option is required to use includes and extends with "relative" paths
      at undefined line 2</p>
  
  <p>STACK: Error:
  [vue-jest] Error: Error: the "filename" option is required to use includes and extends with "relative" paths
      at undefined line 2</p>
  
  <pre><code>at error (/Users/magno.sousa/Documents/playground/vue-test/vuetest/node_modules/vue-jest/lib/throw-error.js:2:9)
  at module.exports (/Users/magno.sousa/Documents/playground/vue-test/vuetest/node_modules/vue-jest/lib/compilers/pug-compiler.js:11:5)
  at getTemplateContent (/Users/magno.sousa/Documents/playground/vue-test/vuetest/node_modules/vue-jest/lib/template-compiler.js:11:12)
  at compileTemplate (/Users/magno.sousa/Documents/playground/vue-test/vuetest/node_modules/vue-jest/lib/template-compiler.js:23:25)
  at Object.module.exports [as process] (/Users/magno.sousa/Documents/playground/vue-test/vuetest/node_modules/vue-jest/lib/process.js:70:29)
  at ScriptTransformer.transformSource (/Users/magno.sousa/Documents/playground/vue-test/vuetest/node_modules/jest-runtime/build/script_transformer.js:247:35)
  at exports.default (/Users/magno.sousa/Documents/playground/vue-test/vuetest/node_modules/jest/node_modules/jest-cli/build/generate_empty_coverage.js:16:105)
  at Object.worker (/Users/magno.sousa/Documents/playground/vue-test/vuetest/node_modules/jest/node_modules/jest-cli/build/reporters/coverage_worker.js:48:84)
  at execMethod (/Users/magno.sousa/Documents/playground/vue-test/vuetest/node_modules/jest-worker/build/child.js:83:29)
  at process.on (/Users/magno.sousa/Documents/playground/vue-test/vuetest/node_modules/jest-worker/build/child.js:40:7)
  </code></pre>
  
  <p>Here is my Vue component</p>
  
  <p><div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
  <div class="snippet-code">
  <pre class="snippet-code-js lang-js prettyprint-override"><code>&lt;template lang="pug"&gt;
    include HelloWorld.pug
  &lt;/template&gt;
  
  &lt;script&gt;
  export default {
    name: 'HelloWorld',
    data () {
      return {
        msg: 'Welcome to Your Vue.js App'
      }
    }
  }
  &lt;/script&gt;</code></pre>
  </div>
  </div>
  </p>
  
  <p>and my jest config file</p>
  
  <p><div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
  <div class="snippet-code">
  <pre class="snippet-code-js lang-js prettyprint-override"><code>const path = require('path')
  
  module.exports = {
    rootDir: path.resolve(__dirname, '../../'),
    'vue-jest': {
      pug: {
        filename: 'pug'
      }
    },
    moduleFileExtensions: [
      'js',
      'json',
      'vue'
    ],
    moduleNameMapper: {
      '^@/(.*)$': '&lt;rootDir&gt;/src/$1'
    },
    transform: {
      '^.+\\.js$': '&lt;rootDir&gt;/node_modules/babel-jest',
      '.*\\.(vue)$': '&lt;rootDir&gt;/node_modules/vue-jest'
    },
    snapshotSerializers: ['&lt;rootDir&gt;/node_modules/jest-serializer-vue'],
    setupFiles: ['&lt;rootDir&gt;/test/unit/setup'],
    coverageDirectory: '&lt;rootDir&gt;/test/unit/coverage',
    collectCoverageFrom: [
      'src/**/*.{js,vue}',
      '!src/main.js',
      '!src/router/index.js',
      '!**/node_modules/**'
    ]
  }</code></pre>
  </div>
  </div>
  </p>
  
  <p>I tried to add the filename option in the jest config but it's not working. Can anyone help out please?</p>