fix service differentiator

Change-Id: I5332074fc0be208abf5714e2a92591a5a817aca4
diff --git a/nova/files/heka.toml b/nova/files/heka.toml
index cb2e3b8..e15af73 100644
--- a/nova/files/heka.toml
+++ b/nova/files/heka.toml
@@ -2,7 +2,7 @@
 type = "LogstreamerInput"
 log_directory = "/var/log/nova"
 file_match = '(?P<Service>.+)\.log\.?(?P<Seq>\d*)$'
-differentiator = ["'nova','_','Service'"]
+differentiator = ['nova','_','Service']
 priority = ["^Index"]
 decoder = "openstack"