++libgit2

Bumped libgit2. Includes a critical fix for alignment issues in ARM platforms (see https://github.com/libgit2/libgit2/issues/2450)

Diff: https://github.com/libgit2/libgit2/compare/3f3d21badda4dbd9c8c8536ba7e34805a3cadd50...9b87998c97fedcf0c22cef28bb0839ecd68c1efd