Fix missing version of yang-maven-plugin

Set the version of yang-maven-plugin to 2.1.8.

Change-Id: I9f8c445ca3923237afb0049ac25705a760a3c5f5
Issue-ID: SDNC-723
Signed-off-by: Enbo Wang <wangenbo@huawei.com>
diff --git a/odlparent/feature-repo-parent/pom.xml b/odlparent/feature-repo-parent/pom.xml
index cd00bd2..5d28339 100644
--- a/odlparent/feature-repo-parent/pom.xml
+++ b/odlparent/feature-repo-parent/pom.xml
@@ -475,6 +475,7 @@
 					<plugin>
 						<groupId>org.opendaylight.yangtools</groupId>
 						<artifactId>yang-maven-plugin</artifactId>
+						<version>2.1.8</version>
 						<dependencies>
 							<dependency>
 								<groupId>org.opendaylight.mdsal</groupId>