In Travis CI ubuntu 14, c# projects fail to build with message: project.assets.json doesn't have a target for '.NETFramework,Version=v4.5' /'.NETCoreApp,Version=v2.1'

I have a solution c# with 5 projects, two of them fail
The solution is built successfully in my machine windows 7.

The first project with target net45 fail with message:

project.assets.json’ doesn’t have a target for ‘.NETCoreApp,Version=v2.1’. Ensure that restore has run and that you have included ‘netcoreapp2.1’

The strange is asking for netcoreapp2.1 but the project is net45

The second project with target netcoreapp2.1 fail with message:

project.assets.json’ doesn’t have a target for ‘.NETFramework,Version=v4.5’.
The strange is asking for net45 but project is netcoreapp2.1

How to resolve that problem?.

The project log is here