bash prompt: combine 'git rev-parse' for detached head

diff --git a/RelNotes b/RelNotes
index 17d37af54951e3179282cad837ee0beb271eb4e9..fce99fb79d16cbeb717ddbe36c7be231a00e4eba 120000 (symlink)
--- a/RelNotes
+++ b/RelNotes
@@ -1 +1 @@
-Documentation/RelNotes/1.7.2.5.txt
\ No newline at end of file
+Documentation/RelNotes/1.8.4.txt
\ No newline at end of file