Bump MartinCostello.BuildKit and Microsoft.NETFramework.ReferenceAssemblies (#876)

Bumps [MartinCostello.BuildKit](https://github.com/martincostello/build-kit) and [Microsoft.NETFramework.ReferenceAssemblies](https://github.com/Microsoft/dotnet). These dependencies needed to be updated together.

Updates `MartinCostello.BuildKit` from 0.3.0 to 0.3.1
- [Release notes](https://github.com/martincostello/build-kit/releases)
- [Commits](martincostello/build-kit@v0.3.0...v0.3.1)

Updates `Microsoft.NETFramework.ReferenceAssemblies` from 1.0.3 to 1.0.3
- [Commits](https://github.com/Microsoft/dotnet/commits)

---
updated-dependencies:
- dependency-name: MartinCostello.BuildKit
  dependency-type: direct:production
  update-type: version-update:semver-patch
- dependency-name: Microsoft.NETFramework.ReferenceAssemblies
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

Directory.Packages.props

@@ -1,6 +1,6 @@
 <Project>
   <ItemGroup>
-    <GlobalPackageReference Include="MartinCostello.BuildKit" Version="0.3.0" />
+    <GlobalPackageReference Include="MartinCostello.BuildKit" Version="0.3.1" />
     <GlobalPackageReference Include="ReferenceTrimmer" Version="3.3.11" PrivateAssets="All" />
     <GlobalPackageReference Include="StyleCop.Analyzers" Version="1.2.0-beta.556" PrivateAssets="All" />
   </ItemGroup>