fixed plugin errors during 'npm test'

`npm test` used to print:
```
> iframely@0.6.0 test /Users/trevorah/Development/trevorah/iframely
> ./node_modules/vows/bin/vows test/main.js --isolate --spec

Error loading plugin /Users/trevorah/Development/trevorah/iframely/plugins/domains/gawker.js [TypeError: Cannot read property 'readability' of undefined]
Error loading plugin /Users/trevorah/Development/trevorah/iframely/plugins/domains/qz.com.js [TypeError: Cannot read property 'readability' of undefined]
Error loading plugin /Users/trevorah/Development/trevorah/iframely/plugins/domains/twitter.status.js [TypeError: Cannot read property 'twitter.status' of undefined]
Error loading plugin /Users/trevorah/Development/trevorah/iframely/plugins/domains/wordpress.com.js [TypeError: Cannot read property 'readability' of undefined]
Error loading plugin /Users/trevorah/Development/trevorah/iframely/plugins/links/article/article.js [TypeError: Cannot read property 'readability' of undefined]
Error loading plugin /Users/trevorah/Development/trevorah/iframely/plugins/links/article/check-article.js [TypeError: Cannot read property 'readability' of undefined]
Error loading plugin /Users/trevorah/Development/trevorah/iframely/plugins/links/oembed-reader.js [TypeError: Cannot read property 'readability' of undefined]

  ♢ Tests

  qik oembed
    ✓ not error
    ✓ has valid oEmbed object
  qik meta
    ✓ not error
    ✓ has meta
  image size
    ✓ has correct size and type
  vimeo oembed
    ✓ not error
    ✓ has valid oEmbed object
   -- plugin redirect (by "htmlparser") http://vimeo.com/63683408
  vimeo meta
    ✓ not error
    ✓ has meta

✓ OK » 9 honored (0.972s)
```
after this patch, you get:
```
> iframely@0.6.0 test /Users/trevorah/Development/trevorah/iframely
> ./node_modules/vows/bin/vows test/main.js --isolate --spec


  ♢ Tests

  image size
    ✓ has correct size and type
  vimeo oembed
    ✓ not error
    ✓ has valid oEmbed object
  qik oembed
    ✓ not error
    ✓ has valid oEmbed object
   -- plugin redirect (by "htmlparser") http://vimeo.com/63683408
  vimeo meta
    ✓ not error
    ✓ has meta
  qik meta
    ✓ not error
    ✓ has meta

✓ OK » 9 honored (0.709s)
```