write_ref_sha1(): only invalidate the loose ref cache

diff --git a/RelNotes b/RelNotes
index 692968f1702044f0474228f2c19f6086568ec9e4..7d9276973af3a8f455778d2ce3ced66167f46801 120000 (symlink)
--- a/RelNotes
+++ b/RelNotes
@@ -1 +1 @@
-Documentation/RelNotes-1.6.6.2.txt
\ No newline at end of file
+Documentation/RelNotes/1.7.8.txt
\ No newline at end of file