pom.xml: Externalise Gerrit version variable

Change-Id: I3e72c293644862f503f8141e4a87d41c01e11e79

pom.xml

diff --git a/pom.xml b/pom.xml
index 351cdd3..25a122d 100644
--- a/pom.xml
+++ b/pom.xml
@@ -38,19 +38,20 @@
 
     <properties>
         <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
+        <gerrit.version>3.0.2</gerrit.version>
     </properties>
 
     <dependencies>
         <dependency>
             <groupId>com.google.gerrit</groupId>
             <artifactId>gerrit-plugin-api</artifactId>
-            <version>3.0.2</version>
+            <version>${gerrit.version}</version>
             <scope>provided</scope>
         </dependency>
         <dependency>
             <groupId>com.google.gerrit</groupId>
             <artifactId>gerrit-acceptance-framework</artifactId>
-            <version>3.0.2</version>
+            <version>${gerrit.version}</version>
             <scope>test</scope>
         </dependency>
         <dependency>