fix(TestBed): TestBed toNodeList and whitespace

[ofagbemi]

I was using the TestBed class and found that the rootElement member wasn't being set properly. After some searching, I found that the problem was with the toNodeList function and the string I was passing to the TestBed's compile function:

String html => '''
  <component>
    <some-directive></some-directive>
  </component>
''';

The node list returned by toNodeList looked something like this

[        
, component,          ]

It looks like toNodeList doesn't play well with whitespace. I got around it by just trimming the string first, but I don't know if that could introduce any other issues down the line.