Bump BBT.Maybe from 2.0.0 to 3.1.0 in /src (#47)

Bumps [BBT.Maybe](https://github.com/bbtsoftware/BBT.Maybe) from 2.0.0 to 3.1.0.
- [Release notes](https://github.com/bbtsoftware/BBT.Maybe/releases)
- [Changelog](https://github.com/bbtsoftware/BBT.Maybe/blob/develop/GitReleaseManager.yaml)
- [Commits](bbtsoftware/BBT.Maybe@2.0.0...3.1.0)

Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Co-authored-by: dependabot-preview[bot] <27856297+dependabot-preview[bot]@users.noreply.github.com>

src/BBT.StructureTools/BBT.StructureTools.csproj

@@ -34,7 +34,7 @@
   </PropertyGroup>
 
   <ItemGroup>
-    <PackageReference Include="BBT.Maybe" Version="2.0.0" />
+    <PackageReference Include="BBT.Maybe" Version="3.1.0" />
     <PackageReference Include="BBT.StrategyPattern" Version="1.0.0" />
     <PackageReference Include="Microsoft.CodeAnalysis.FxCopAnalyzers" Version="2.9.4">
       <PrivateAssets>all</PrivateAssets>