write_ref_sha1(): only invalidate the loose ref cache

diff --git a/RelNotes b/RelNotes
index 115c33553bb99a5ac6c21c2ac0f33ab7b48a4901..7d9276973af3a8f455778d2ce3ced66167f46801 120000 (symlink)
--- a/RelNotes
+++ b/RelNotes
@@ -1 +1 @@
-Documentation/RelNotes-1.6.5.6.txt
\ No newline at end of file
+Documentation/RelNotes/1.7.8.txt
\ No newline at end of file