Update version of PyYAML

Change-Id: I80b9ca580f8bb831d388cc7ad30c43211b4b51ac
Signed-off-by: Mark Beierl <mark.beierl@canonical.com>
diff --git a/requirements-dev.txt b/requirements-dev.txt
index b46cedb..31c31d4 100644
--- a/requirements-dev.txt
+++ b/requirements-dev.txt
@@ -294,7 +294,7 @@
     # via flask-babel
 pytzdata==2020.1
     # via pendulum
-pyyaml==5.4.1
+pyyaml==6.0.1
     # via
     #   -r https://osm.etsi.org/gitweb/?p=osm/common.git;a=blob_plain;f=requirements.txt;hb=master
     #   apispec