Can't remove headers after they are sent (ci tests)
```
018-06-12T07:18:43.039Z gate INFO request ::ffff:127.0.0.1 GET /auth/mock 302 8.047 ms
2018-06-12T07:18:43.046Z gate INFO request ::ffff:127.0.0.1 GET /mockOAuth/auth?response_type=code&redirect_uri=http%3A%2F%2Flocalhost%3A8000%2Fauth%2Fmock%2Fcallback&scope=user%3Aemail%20repo%20write%3Arepo_hook&client_id=MOCKCLIENTID 302 1.765 ms
Error: Can't remove headers after they are sent
at ServerResponse.removeHeader (_http_outgoing.js:574:11)
at ServerResponse.send (/builds/venture-api/gate/node_modules/express/lib/response.js:210:10)
at ServerResponse.json (/builds/venture-api/gate/node_modules/express/lib/response.js:267:15)
at module.exports (/builds/venture-api/gate/middleware/responseSender.js:1:3190)
at /builds/venture-api/gate/node_modules/express-async-errors/index.js:17:20
at Layer.handle [as handle_request] (/builds/venture-api/gate/node_modules/express/lib/router/layer.js:95:5)
at trim_prefix (/builds/venture-api/gate/node_modules/express/lib/router/index.js:317:13)
at /builds/venture-api/gate/node_modules/express/lib/router/index.js:284:7
at Function.process_params (/builds/venture-api/gate/node_modules/express/lib/router/index.js:335:12)
at next (/builds/venture-api/gate/node_modules/express/lib/router/index.js:275:10)
at Layer.handle [as handle_request] (/builds/venture-api/gate/node_modules/express/lib/router/layer.js:91:12)
at trim_prefix (/builds/venture-api/gate/node_modules/express/lib/router/index.js:317:13)
at /builds/venture-api/gate/node_modules/express/lib/router/index.js:284:7
at Function.process_params (/builds/venture-api/gate/node_modules/express/lib/router/index.js:335:12)
at Immediate.next (/builds/venture-api/gate/node_modules/express/lib/router/index.js:275:10)
at Immediate._onImmediate (/builds/venture-api/gate/node_modules/express/lib/router/index.js:635:15)
at runCallback (timers.js:812:20)
at tryOnImmediate (timers.js:768:5)
at processImmediate [as _immediateCallback] (timers.js:745:5)
2018-06-12T07:18:43.071Z gate INFO request ::ffff:127.0.0.1 POST /mockOAuth/token 200 15.643 ms
```
issue