Error after canceling `ember try:one`

When running a single scenario such as:

```
ember try:one ember-canary --- ember s --port=0
```

When you close the server (via `ctrl-c` generally), the following error is emitted:

```
Error!
TypeError: Cannot read property 'result' of undefined
TypeError: Cannot read property 'result' of undefined
at results.forEach (/Users/rjackson/src/open-source/ember-test-helpers/node_modules/ember-try/lib/utils/result-summary.js:18:20)
at Array.forEach ()
at Class.print (/Users/rjackson/src/open-source/ember-test-helpers/node_modules/ember-try/lib/utils/result-summary.js:17:18)
at Class._printResults (/Users/rjackson/src/open-source/ember-test-helpers/node_modules/ember-try/lib/tasks/try-each.js:129:54)
at task._optionallyCleanup.then (/Users/rjackson/src/open-source/ember-test-helpers/node_modules/ember-try/lib/tasks/try-each.js:36:14)
at tryCatch (/Users/rjackson/src/open-source/ember-test-helpers/node_modules/rsvp/dist/rsvp.js:525:12)
at invokeCallback (/Users/rjackson/src/open-source/ember-test-helpers/node_modules/rsvp/dist/rsvp.js:538:13)
at publish (/Users/rjackson/src/open-source/ember-test-helpers/node_modules/rsvp/dist/rsvp.js:508:7)
at flush (/Users/rjackson/src/open-source/ember-test-helpers/node_modules/rsvp/dist/rsvp.js:2415:5)
at process._tickCallback (internal/process/next_tick.js:150:11)
```