Always remove .gitmodules (#2)

This is a dirty solution which will only work for a repo with one
submodule and no history of ever having another, but hey, the goal of
our first release is to solve a specific problem I have, not to please
everyone. We have issues filed--we'll get there eventually.

CHANGELOG.md

@@ -12,7 +12,8 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 First public release.
 
 ###Added
-- Merges submodules that reside in the repository's root
+- Merges a single submodule that resides in the repository's root
+- Removes `.gitmodules`
 - User can provide mappings from missing commit IDs to existing ones
 
 

src/main.rs

@@ -511,10 +511,15 @@ fn replace_submodule_dir<'repo>(repo: &'repo Repository,
                                 -> Tree<'repo> {
     let mut treebuilder = repo.treebuilder(Some(&tree))
         .expect("Couldn't create TreeBuilder");
+
     treebuilder.remove(submodule_path)
         .expect("Couldn't remove submodule path from TreeBuilder");
     treebuilder.insert(submodule_path, *subtree_id, 0o040000)
         .expect("Couldn't add submodule as a subdir to TreeBuilder");
+
+    treebuilder.remove(".gitmodules")
+        .expect("Couldn't remove .gitmodules from TreeBuilder");
+
     let new_tree_id = treebuilder.write()
         .expect("Couldn't write TreeBuilder into a Tree");
     let new_tree = repo.find_tree(new_tree_id)