Broken YAML files on package import

[DuFF14]

This issue is resolved by the Unity editor so no functionality is broken, but I haven't been able to fix whatever is wrong with the recently updated VRDisplayTracked and VRFirstPersonController prefabs.

To reproduce:

• Import a recent binary like Build #630 http://access.osvr.com/binary/osvr-unity

alternatively:

• Check out this repo's master branch
• Import the Plugins folder only from a recent binary, to get the updated DLLs
• Right click on OSVRUnity folder and export package.
• Import the new package into a new project. This produces the same errors as CI build.

I've tried re-creating the prefabs, deleting meta files, merging a branch that undid the updates (then updated the prefabs again), and manually editing the .prefab files. I am out of ideas for now, other than reverting commits to see if that error goes away, but since everything works on import, I'll not go there just yet...

[DuFF14]

fixed by #227