Fix to activate command

Signed-off-by: Andrew Geissler <geissonator@yahoo.com>
diff --git a/openbmc-sfw b/openbmc-sfw
index 192869a..5e95473 100755
--- a/openbmc-sfw
+++ b/openbmc-sfw
@@ -58,7 +58,7 @@
 
     def activate_image(self, image_id):
         r = self.session.put(self.url + "/xyz/openbmc_project/software/" + image_id + "/attr/RequestedActivation", 
-                             data="xyz.openbmc_project.Software.Activation.RequestedActivations.Active",
+                             json={'data': 'xyz.openbmc_project.Software.Activation.RequestedActivations.Active'},
                              verify=False)
         
         j = r.json()