setup: set env $GIT_WORK_TREE when work tree is set, like $GIT_DIR

diff --git a/RelNotes b/RelNotes
index 1efc120fe0bdb1a207a1e93ba97c0a082fd32d78..5696e88ad5f86cac0e7095469e8d705337c91e2e 120000 (symlink)
--- a/RelNotes
+++ b/RelNotes
@@ -1 +1 @@
-Documentation/RelNotes/1.8.5.2.txt
\ No newline at end of file
+Documentation/RelNotes/2.0.5.txt
\ No newline at end of file