Update python-libjuju version to 2.9.42.4

Change-Id: Ie9b42f14c59aa9690afde319e29cebbf3de173b1
Signed-off-by: Guillermo Calvino <guillermo.calvino@canonical.com>
diff --git a/requirements.in b/requirements.in
index 03898e9..85f139a 100644
--- a/requirements.in
+++ b/requirements.in
@@ -13,7 +13,7 @@
 #     limitations under the License.
 
 async-timeout<4
-juju==3.0.0
+juju==2.9.42.4
 kubernetes
 motor==1.3.1
 pyasn1