cache invalidation when removing invites

{"name":"mservice","hostname":"fad50e30651d","pid":1,"level":50,"err":{"message":"404","name":"Error","stack":"Error: 404\n    at redis.hgetall.then.then.data (/src/node_modules/ms-token/lib/backends/redis/redis.js:149:15)\n    at tryCatcher (/src/node_modules/bluebird/js/release/util.js:16:23)\n    at Promise._settlePromiseFromHandler (/src/node_modules/bluebird/js/release/promise.js:510:31)\n    at Promise._settlePromise (/src/node_modules/bluebird/js/release/promise.js:567:18)\n    at Promise._settlePromise0 (/src/node_modules/bluebird/js/release/promise.js:612:10)\n    at Promise._settlePromises (/src/node_modules/bluebird/js/release/promise.js:691:18)\n    at Async._drainQueue (/src/node_modules/bluebird/js/release/async.js:138:16)\n    at Async._drainQueues (/src/node_modules/bluebird/js/release/async.js:148:10)\n    at Immediate.Async.drainQueues (/src/node_modules/bluebird/js/release/async.js:17:14)\n    at runCallback (timers.js:574:20)\n    at tryOnImmediate (timers.js:554:5)\n    at processImmediate [as _immediateCallback] (timers.js:533:5)"},"msg":"404","time":"2016-09-14T21:19:52.563Z","v":0}

Start with the Redis-related stack trace at /src/node_modules/ms-token/lib/backends/redis/redis.js:149:15 and trace how removing invites interacts with cache invalidation. Reproduce the reported 404 and identify the relevant invite-removal path; done means removing an invite no longer leaves the cache in an invalid state.