Update version of PyYAML

Change-Id: I80c3238d9a7c0985fc261900507ff2e2d0487056
Signed-off-by: Mark Beierl <mark.beierl@canonical.com>
diff --git a/requirements.in b/requirements.in
index 94c2eb9..128194b 100644
--- a/requirements.in
+++ b/requirements.in
@@ -15,4 +15,4 @@
 
 pyang
 pyangbind
-pyyaml==5.4.1
\ No newline at end of file
+pyyaml>6
\ No newline at end of file