Set velocity view content type to HTML.

Previously the content type was not set and it
was left to the Browser to properly understand the
result output. That sometimes generated a plaintext
HTML in some browsers.

Change-Id: I5c9fd2cf5444dcd343d0d378df6df9353c06cf2c

github-plugin/src/main/java/com/googlesource/gerrit/plugins/github/velocity/VelocityViewServlet.java

diff --git a/github-plugin/src/main/java/com/googlesource/gerrit/plugins/github/velocity/VelocityViewServlet.java b/github-plugin/src/main/java/com/googlesource/gerrit/plugins/github/velocity/VelocityViewServlet.java
index b17f858..21a88e7 100644
--- a/github-plugin/src/main/java/com/googlesource/gerrit/plugins/github/velocity/VelocityViewServlet.java
+++ b/github-plugin/src/main/java/com/googlesource/gerrit/plugins/github/velocity/VelocityViewServlet.java
@@ -16,6 +16,7 @@
 import java.io.IOException;
 import java.util.Map.Entry;
 
+import javax.mail.internet.ContentType;
 import javax.servlet.ServletException;
 import javax.servlet.ServletRequest;
 import javax.servlet.ServletResponse;
@@ -88,6 +89,7 @@
       Template template = velocityRuntime.getTemplate(pathInfo, "UTF-8");
       VelocityContext context = initVelocityModel(req).getContext();
       context.put("request", req);
+      resp.setHeader("content-type", "text/html");
       template.merge(context, resp.getWriter());
     } catch (ResourceNotFoundException e) {
       log.error("Cannot load velocity template " + pathInfo, e);