title: (php) sqlite in-memory db gets "could not find driver" error
body: <p>I have installed php7.1.7 in my Windows. New Laravel 5.4 install; tried configuring phpunit to use in-memory sqlite db as such </p>
  
  <pre><code>    &lt;env name="APP_ENV" value="testing"/&gt;
      &lt;env name="DB_CONNECTION" value="sqlite"/&gt;
      &lt;env name="DB_DATABASE" value=":memory:"/&gt;
  </code></pre>
  
  <p>running vendor/bin/phpunit fails with:</p>
  
  <blockquote>
    <p>1) Tests\Feature\ThreadsTest::a_user_can_browse_threads
    Illuminate\Database\QueryException: could not find driver (SQL: select * from sqlite_master where type = 'table' and name = migrations)</p>
  </blockquote>
  
  <p>If I try another value for DB_DATABASE, other than ':memory:' it fails with a database not found error, but not the 'could not find driver' error </p>