Upgrades LibGit2Sharp to latest preview to fix issue preventing it to work on ubuntu:20.04

See libgit2/libgit2sharp#1747

Author: 8

src/GitContributors/GitContributors.fsproj

@@ -6,7 +6,7 @@
     <PackAsTool>true</PackAsTool>
     <ToolCommandName>git-contributor</ToolCommandName>
     <PackageOutputPath>./nupkg</PackageOutputPath>
-    <Version>0.2.0</Version>
+    <Version>0.3.0</Version>
   </PropertyGroup>
 
   <ItemGroup>
@@ -23,7 +23,7 @@
   </ItemGroup>
 
   <ItemGroup>
-    <PackageReference Include="LibGit2Sharp" Version="0.26.2" />
+    <PackageReference Include="LibGit2Sharp" Version="0.27.0-preview-0116" />
     <PackageReference Include="Mono.Options" Version="6.6.0.161" />
     <PackageReference Include="Spectre.Console" Version="0.40.0" />
   </ItemGroup>