Add LF before missing contributor agreement error

This forces the text to start on the next line, so that the client
side added "remote: error: " prefix does not cause an incorrect
line wrapping of the message.

Change-Id: I11d1b154a6f55550a71dc35315fe62efa5a9a263

gerrit-httpd/src/main/java/com/google/gerrit/httpd/ProjectServlet.java

@@ -315,7 +315,7 @@ public class ProjectServlet extends GitServlet {
       if (s != Capable.OK) {
         GitSmartHttpTools.sendError((HttpServletRequest) request,
             (HttpServletResponse) response, HttpServletResponse.SC_FORBIDDEN,
-            s.getMessage());
+            "\n" + s.getMessage());
         return;
       }