Upgrading PyYaml due to new juju package

Change-Id: Idce6235e9bdd033d16d207734c9e1ddd0ed0453b
Signed-off-by: lavado <glavado@whitestack.com>
diff --git a/requirements.txt b/requirements.txt
index 6215643..29ee06a 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -23,7 +23,7 @@
 python-keystoneclient==3.15.*
 six==1.11.*
 peewee==3.8.*
-pyyaml==3.*
+pyyaml>=5.1.2
 prometheus_client==0.4.*
 gnocchiclient==7.0.*
 pymysql==0.9.*