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

diff --git a/RelNotes b/RelNotes
index 4567ad64fe794a21e1d041ddf766c55cb2c1fc7a..5696e88ad5f86cac0e7095469e8d705337c91e2e 120000 (symlink)
--- a/RelNotes
+++ b/RelNotes
@@ -1 +1 @@
-Documentation/RelNotes/1.7.7.3.txt
\ No newline at end of file
+Documentation/RelNotes/2.0.5.txt
\ No newline at end of file