Submodule libgit2sharp updated

Submodule libgit2sharp:
    > d9ecbae - Update libgit2 binaries to e87d9d3
    > 7b38c3c - Garbage collection protection
    > b65f966 - Fix UpdateLibgit2ToSha.ps1 path context handling
    > e143eaf - Add RewriteHistoryOptions.OnSucceeding and OnError
    > c7c12e7 - Enforce symlink creation and parsing test coverage
    > af11289 - Check autocrlf in filtered text test
    > 0c4780b - Note that Blob.Size is size of raw content
    > e027739 - Ensure Blob.ContentStream() has Length
    > 71090d3 - Deprecate Blob.Content
    > 2e201d5 - Rename Blob.ContentAsText() as Blob.GetContentText()
    > da32029 - Rename Blob.ContentStream() as Blob.GetContentStream()
    > 36945a9 - Push down Stream related helpers into BaseFixture
    > 2bb26a5 - Teach BaseFixture.Touch() to accept Streams
    > 7af5c60 - Teach LambdaEqualityHelper to deal with null equality contribution
    > fc78c72 - Add meta test to find missing [Fact]/[Theory]