Add context path when redirecting to /login/

PR: https://github.com/thesamet/gerrit-saml-plugin/pull/3
Change-Id: Ic506ce5d53ca2ed8ed56c9e9d63e3df51ba700a7
diff --git a/src/main/java/com/thesamet/gerrit/plugins/saml/SamlWebFilter.java b/src/main/java/com/thesamet/gerrit/plugins/saml/SamlWebFilter.java
index 6731571..1717bf4 100644
--- a/src/main/java/com/thesamet/gerrit/plugins/saml/SamlWebFilter.java
+++ b/src/main/java/com/thesamet/gerrit/plugins/saml/SamlWebFilter.java
@@ -131,7 +131,7 @@
             if (null == redirectUri || redirectUri.isEmpty()) {
                 redirectUri = "/";
             }
-            context.getResponse().sendRedirect(redirectUri);
+            context.getResponse().sendRedirect(context.getRequest().getContextPath() + redirectUri);
         } else {
             signout(context.getRequest(), context.getResponse());
         }