Add missing helper tag fallback attr. Closes #520
Add missing helper tag fallback attr. Closes #520

This commit add missing fallback test attribute to script tag helper.
This fix will remove missing fallback attribute warning from console
for this specific tag helper.

aspnet/AspNetCore,aspnet/AspNetCore,aspnet/AspNetCore,aspnet/AspNetCore,aspnet/AspNetCore,aspnet/AspNetCore,aspnet/AspNetCore,aspnet/AspNetCore,aspnet/AspNetCore