Pin older versions of packages to restore
Pin older versions of packages to restore

With the RTM version of System.Linq.Expressions and no mention of the
other packages added here, restore of the runtime packages failed with
these errors:

```
Errors in o:\msbuild\targets\runtimeDependencies\project.json
    System.Linq.Expressions 4.1.0 provides a compile-time reference assembly for System.Linq.Expressions on .NETCoreApp,Version=v1.0, but there is no run-time assembly compatible with osx.10.10-x64.
    System.Linq 4.1.0 provides a compile-time reference assembly for System.Linq on .NETCoreApp,Version=v1.0, but there is no run-time assembly compatible with osx.10.10-x64.
    System.Net.Http 4.1.0 provides a compile-time reference assembly for System.Net.Http on .NETCoreApp,Version=v1.0, but there is no run-time assembly compatible with osx.10.10-x64.
    System.Text.RegularExpressions 4.1.0 provides a compile-time reference assembly for System.Text.RegularExpressions on .NETCoreApp,Version=v1.0, but there is no run-time assembly compatible with osx.10.10-x64.
    One or more packages are incompatible with .NETCoreApp,Version=v1.0 (osx.10.10-x64).
    System.Linq.Expressions 4.1.0 provides a compile-time reference assembly for System.Linq.Expressions on .NETCoreApp,Version=v1.0, but there is no run-time assembly compatible with ubuntu.14.04-x64.
    System.Linq 4.1.0 provides a compile-time reference assembly for System.Linq on .NETCoreApp,Version=v1.0, but there is no run-time assembly compatible with ubuntu.14.04-x64.
    System.Net.Http 4.1.0 provides a compile-time reference assembly for System.Net.Http on .NETCoreApp,Version=v1.0, but there is no run-time assembly compatible with ubuntu.14.04-x64.
    System.Text.RegularExpressions 4.1.0 provides a compile-time reference assembly for System.Text.RegularExpressions on .NETCoreApp,Version=v1.0, but there is no run-time assembly compatible with ubuntu.14.04-x64.
    One or more packages are incompatible with .NETCoreApp,Version=v1.0 (ubuntu.14.04-x64).
    System.Linq.Expressions 4.1.0 provides a compile-time reference assembly for System.Linq.Expressions on .NETCoreApp,Version=v1.0, but there is no run-time assembly compatible with win7-x64.
    System.Linq 4.1.0 provides a compile-time reference assembly for System.Linq on .NETCoreApp,Version=v1.0, but there is no run-time assembly compatible with win7-x64.
    System.Text.RegularExpressions 4.1.0 provides a compile-time reference assembly for System.Text.RegularExpressions on .NETCoreApp,Version=v1.0, but there is no run-time assembly compatible with win7-x64.
    One or more packages are incompatible with .NETCoreApp,Version=v1.0 (win7-x64).
    System.Linq.Expressions 4.1.0 provides a compile-time reference assembly for System.Linq.Expressions on .NETCoreApp,Version=v1.0, but there is no run-time assembly compatible with win7-x86.
    System.Linq 4.1.0 provides a compile-time reference assembly for System.Linq on .NETCoreApp,Version=v1.0, but there is no run-time assembly compatible with win7-x86.
    System.Text.RegularExpressions 4.1.0 provides a compile-time reference assembly for System.Text.RegularExpressions on .NETCoreApp,Version=v1.0, but there is no run-time assembly compatible with win7-x86.
    One or more packages are incompatible with .NETCoreApp,Version=v1.0 (win7-x86).
```

AndyGerlicher/msbuild,mono/msbuild,sean-gilliam/msbuild,jeffkl/msbuild,mono/msbuild,cdmihai/msbuild,cdmihai/msbuild,rainersigwald/msbuild,Microsoft/msbuild,chipitsine/msbuild,rainersigwald/msbuild,rainersigwald/msbuild,Microsoft/msbuild,Microsoft/msbuild,jeffkl/msbuild,AndyGerlicher/msbuild,jeffkl/msbuild,cdmihai/msbuild,jeffkl/msbuild,chipitsine/msbuild,chipitsine/msbuild,chipitsine/msbuild,AndyGerlicher/msbuild,mono/msbuild,cdmihai/msbuild,AndyGerlicher/msbuild,mono/msbuild,rainersigwald/msbuild,Microsoft/msbuild,sean-gilliam/msbuild,sean-gilliam/msbuild,sean-gilliam/msbuild