Update voluptuous requirement

Reading historical voluptuous docs it appears that the change to dict
handling occurred in the new 0.10.2 release. There are no earlier 0.10
releases to check against so just require voluptuous>=0.10.2.

Change-Id: I5ade4a8c2d03d5519ae1ed95e133717d5c28d0ad
diff --git a/requirements.txt b/requirements.txt
index c7e059a..974b77f 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -9,7 +9,7 @@
 python-daemon>=2.0.4,<2.1.0
 extras
 statsd>=1.0.0,<3.0
-voluptuous>=0.7
+voluptuous>=0.10.2
 gear>=0.5.7,<1.0.0
 apscheduler>=3.0
 PrettyTable>=0.6,<0.8