convertTree(depTree, tree, pathCache) {
		for (const key in depTree) {
			const id = this.processPath(key, pathCache);

			if (!tree[id]) {
				tree[id] = [];

				for (const dep in depTree[key]) {
					tree[id].push(this.processPath(dep, pathCache));
				}

				this.convertTree(depTree[key], tree, pathCache);
			}
		}

		return tree;
	}
Convert deep tree produced by dependency-tree to a
shallow (one level deep) tree used by madge.
@param  {Object} depTree
@param  {Object} tree
@param  {Object} pathCache
@return {Object}