Fix name of TextureReader property

[lilleyse]

A small mistake from b891542. The property inside TextureReader should be called texture not textureReader.

[cesium-concierge]

Thanks for the pull request @lilleyse!

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• ❔ Unit tests were not updated.
  • Make sure you've updated tests to reflect your changes, added tests for any new code, and ran the code coverage tool.

Reviewers, don't forget to make sure that:

• Cesium Viewer works.
• Works in 2D/CV.
• Works (or fails gracefully) in IE11.

[ptrgags]

Nice catch, @lilleyse I'll merge once CI passes!

[ptrgags]

Thanks @lilleyse!