Obrigado Marcelo!
Fiz a mudança para a 4.5.2.
Então segui o tópico https://cursos.alura.com.br/forum/topico-instalacao-do-entity-no-visual-studio-2012-26932
que diz que eu deveria fazer o Uninstall do EF 6.1.3 e depois instalar:
Install-Package EntityFramework.MicrosoftSqlServer -Version 7.0.0-rc1-final -Pre
Install-Package EntityFramework.Commands -Version 7.0.0-rc1-final -pre
Mas ambos os comandos produziram basicamente o mesmo erro de dependência:
PM> Install-Package EntityFramework.MicrosoftSqlServer -Version 7.0.0-rc1-final -Pre
Attempting to resolve dependency 'EntityFramework.Relational (≥ 7.0.0-rc1-final)'.
Attempting to resolve dependency 'EntityFramework.Core (≥ 7.0.0-rc1-final)'.
Install-Package : 'EntityFramework.Core' already has a dependency defined for 'Ix-Async'.
At line:1 char:1
+ Install-Package EntityFramework.MicrosoftSqlServer -Version 7.0.0-rc1-final -Pre
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ CategoryInfo : NotSpecified: (:) [Install-Package], InvalidOperationException
+ FullyQualifiedErrorId : NuGetCmdletUnhandledException,NuGet.PowerShell.Commands.InstallPackageCommand
Install-Package EntityFramework.Commands -Version 7.0.0-rc1-final -pre
Attempting to resolve dependency 'EntityFramework.Relational.Design (≥ 7.0.0-rc1-final)'.
Install-Package : 'EntityFramework.Relational.Design' already has a dependency defined for 'EntityFramework.Relational'.
At line:1 char:1
+ Install-Package EntityFramework.Commands -Version 7.0.0-rc1-final -pre
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ CategoryInfo : NotSpecified: (:) [Install-Package], InvalidOperationException
+ FullyQualifiedErrorId : NuGetCmdletUnhandledException,NuGet.PowerShell.Commands.InstallPackageCommand
Alguma sugestão?