Bump to Gerrit 2.15.6

Change-Id: I68048cb1e31c72075aac85b1cd328fffa888c99a

github-oauth/pom.xml

diff --git a/github-oauth/pom.xml b/github-oauth/pom.xml
index 005e5a5..af9dd64 100644
--- a/github-oauth/pom.xml
+++ b/github-oauth/pom.xml
@@ -21,7 +21,7 @@
   <parent>
     <groupId>com.googlesource.gerrit.plugins.github</groupId>
     <artifactId>github-parent</artifactId>
-    <version>2.15.3</version>
+    <version>2.15.6</version>
   </parent>
   <artifactId>github-oauth</artifactId>
   <name>Gerrit Code Review - GitHub OAuth login</name>

github-plugin/pom.xml

diff --git a/github-plugin/pom.xml b/github-plugin/pom.xml
index 201d030..fd5b311 100644
--- a/github-plugin/pom.xml
+++ b/github-plugin/pom.xml
@@ -20,7 +20,7 @@
   <parent>
     <artifactId>github-parent</artifactId>
     <groupId>com.googlesource.gerrit.plugins.github</groupId>
-    <version>2.15.3</version>
+    <version>2.15.6</version>
   </parent>
 
   <artifactId>github-plugin</artifactId>

pom.xml

diff --git a/pom.xml b/pom.xml
index dcc8ef6..bb53b65 100644
--- a/pom.xml
+++ b/pom.xml
@@ -18,7 +18,7 @@
   <modelVersion>4.0.0</modelVersion>
   <groupId>com.googlesource.gerrit.plugins.github</groupId>
   <artifactId>github-parent</artifactId>
-  <version>2.15.3</version>
+  <version>2.15.6</version>
   <name>Gerrit Code Review - GitHub integration</name>
   <url>http://www.gerritforge.com</url>
   <packaging>pom</packaging>