Change bbb-lti port so no conflict with tomcat7

bbb-lti/lti.nginx

        # Handle request to bbb-web running within Tomcat.  This is for
        # the BBB-API and Presentation.
        location /lti {
-           proxy_pass         http://127.0.0.1:8080;
+           proxy_pass         http://127.0.0.1:8081;
            proxy_redirect     default;
            proxy_set_header   X-Forwarded-For   $proxy_add_x_forwarded_for;
            proxy_set_header   X-Forwarded-Proto $scheme;