sensorlog_lite: Add missing dependency to Makefile.

Change-Id: Ic16418c104255159c7366c063496fef8aad8d458
diff --git a/go/src/v.io/x/sensorlog/Makefile b/go/src/v.io/x/sensorlog/Makefile
index 9b57e66..84bb5a2 100644
--- a/go/src/v.io/x/sensorlog/Makefile
+++ b/go/src/v.io/x/sensorlog/Makefile
@@ -17,6 +17,7 @@
 	jiri go install v.io/x/ref/services/mounttable/mounttabled
 	jiri go install v.io/x/ref/services/syncbase/syncbased
 	jiri go install v.io/x/ref/services/agent/vbecome
+	jiri go install v.io/x/ref/cmd/principal
 
 .PHONY: test
 test: