Update Templates To Use Preview 3

[agniuks]

WindowsAppSDK-Samples/Templates/VSIX/Directory.Build.props

Line 8 in fbcbdeb

<WindowsAppSdkVersion Condition="'$(WindowsAppSdkVersion)' == ''">1.0.0-preview2</WindowsAppSdkVersion>

I believe this should reference 1.0.0-preview3 instead, no?

[angelazhangmsft]

We plan to update all the samples/templates to 1.0.0 (GA) next week.

[angelazhangmsft]

The templates have been updated to 1.0.0 and are available for download here!