Fix bug 1216: Remove machines only for native charms

Updates revision of Python libjuju to 2.8.4

Change-Id: I3f41eead305349eba5d404f5f3d61d33f0536aca
Signed-off-by: David Garcia <david.garcia@canonical.com>
diff --git a/requirements.txt b/requirements.txt
index 0393d2d..45b6133 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -13,7 +13,7 @@
 #     limitations under the License.
 
 git+https://osm.etsi.org/gerrit/osm/common.git#egg=osm-common
-juju==2.8.2
+juju==2.8.4
 paramiko
 pyasn1>=0.4.4
 kubernetes==10.0.1