Merge pull request #1494 from Athas/add-directory-tree

Bring back directory-tree.

build-constraints.yaml

@@ -2211,6 +2211,9 @@ packages:
         - gi-pango == 1.0.3
         - haskell-gi
 
+    "Brandon Simmons <brandon.m.simmons@gmail.com>":
+        - directory-tree
+
     "Ian Grant Jeffries <ian@housejeffries.com> @seagreen":
         - hjsonpointer
         - hjsonschema
@@ -2582,6 +2585,9 @@ expected-test-failures:
     # isn't always the case (e.g., build server)
     - happy
 
+    # https://github.com/jberryman/directory-tree/issues/4
+    - directory-tree
+
     # https://github.com/ndmitchell/hoogle/issues/101
     - hoogle