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Description

Fixes #475

git-ls-tree returns three types of objects: commits, blobs and trees. git ls-tree returns a commit in place of a submodule tree to indicate the commit SHA in the submodule's repository that is linked into the containing repository.

The implementation of Git::Lib#ls_tree raised an error when git ls-tree returns a commit. This PR changes the implementation so that the commit is returned in the Hash returned (from the test case):

{
  "blob" => {
    ".gitmodules" =>{ mode: "100644", sha: "caff6b7d44973f53e3e0cf31d0d695188b19aec6" },
    "README.md" => { mode: "100644", sha: "ab1bc6e140b700e97253b02e4ca117abe068a73f" }
    },
  "tree" => { },
  "commit" => {
    "submodule" => { mode: "160000", sha: "31b05441cda227c0531d659a13b7e10ce3ba8754" }
  }
}