Update SimpleColorPickerPage.xaml

[alwinSie]

Description of Change

At the end of the Value property at the three UISlider was a curly brace missing (lines 51 - 53).

Pull Request Checklist

• Rebased on top of master at time of the pull request.
• Changes adhere to coding standard in the sample.
• Consolidated NuGet packages across all projects in the sample (when changing existing package versions).
• Tested changes on the appropriate platforms (all platforms if changing the library code).

[davidbritch]

Thanks for the fix @alwinSie