git diff too slow for a file

diff --git a/RelNotes b/RelNotes
index f8e49a5070afc21fbd3db9320841300fe93c570f..a9713ed41272daec5145d6b11091ea84d6469c67 120000 (symlink)
--- a/RelNotes
+++ b/RelNotes
@@ -1 +1 @@
-Documentation/RelNotes-1.6.4.txt
\ No newline at end of file
+Documentation/RelNotes-1.7.0.6.txt
\ No newline at end of file