Bug 1926: Update version of Six

The IM now uses six 1.16.0, so the requirements-dev.txt needs to be
updated to match

Additional dependencies updated:
  lxml
  pyang
  idna
  requests

Fixes bug 1926

Change-Id: I7d8f9ca9a0fd5e0d0e2bdb1900ef247a5b41fccc
Signed-off-by: beierlm <mark.beierl@canonical.com>
diff --git a/requirements-dev.txt b/requirements-dev.txt
index 755da60..a5862bc 100644
--- a/requirements-dev.txt
+++ b/requirements-dev.txt
@@ -30,7 +30,7 @@
     # via
     #   -r https://osm.etsi.org/gitweb/?p=osm/common.git;a=blob_plain;f=requirements.txt;hb=master
     #   aiokafka
-lxml==4.6.3
+lxml==4.7.1
     # via
     #   -r https://osm.etsi.org/gitweb/?p=osm/IM.git;a=blob_plain;f=requirements.txt;hb=master
     #   pyang
@@ -39,7 +39,7 @@
     # via -r requirements-dev.in
 osm-im @ git+https://osm.etsi.org/gerrit/osm/IM.git@master
     # via -r requirements-dev.in
-pyang==2.4.0
+pyang==2.5.2
     # via
     #   -r https://osm.etsi.org/gitweb/?p=osm/IM.git;a=blob_plain;f=requirements.txt;hb=master
     #   pyangbind
@@ -57,7 +57,7 @@
     # via
     #   -r https://osm.etsi.org/gitweb/?p=osm/IM.git;a=blob_plain;f=requirements.txt;hb=master
     #   pyangbind
-six==1.15.0
+six==1.16.0
     # via
     #   -r https://osm.etsi.org/gitweb/?p=osm/IM.git;a=blob_plain;f=requirements.txt;hb=master
     #   pyangbind