Update Gerrit API version to 2.8 in pom.xml

Change-Id: I603255b0e07e15a85c063e1f7a6640911096f873

pom.xml

diff --git a/pom.xml b/pom.xml
index ba5ac6c..1515c32 100644
--- a/pom.xml
+++ b/pom.xml
@@ -22,7 +22,7 @@
   <groupId>com.googlesource.gerrit.plugins.reviewnotes</groupId>
   <artifactId>reviewnotes</artifactId>
   <packaging>jar</packaging>
-  <version>2.8-SNAPSHOT</version>
+  <version>2.8</version>
   <name>reviewnotes</name>
 
   <properties>