Fix gRPC dependency

Change-Id: Iddebec60218b555d8ffe39fcabd3daad0b776218
diff --git a/drivers/gnmi/pom.xml b/drivers/gnmi/pom.xml
index 7614d81..7f0cf54 100644
--- a/drivers/gnmi/pom.xml
+++ b/drivers/gnmi/pom.xml
@@ -46,7 +46,7 @@
         <dependency>
             <groupId>io.grpc</groupId>
             <artifactId>grpc-netty</artifactId>
-            <version>1.3.1</version>
+            <version>${grpccore.version}</version>
         </dependency>
 
         <!-- protocols/gnmi/api missing -->