Fixed!
I simply added PackagesConfig
element to .nuget/NuGet.targets
:
<PropertyGroup Condition=" '$(OS)' != 'Windows_NT'">
<!-- We need to launch nuget.exe with the mono command if we're not on windows -->
<NuGetToolsPath>$(SolutionDir).nuget</NuGetToolsPath>
++++<PackagesConfig>packages.config</PackagesConfig>
</PropertyGroup>