Fix tests

[blag]

For PR #200 it looked like the build passed. But looking at the individual jobs:

...
  141 passing (482ms)
  5 failing
  1) SparkFormatter
       should normalize the addressee:
     AssertionError: expected undefined to be a string
      at Context.<anonymous> (test/test-formatdata.js:406:26)
  
  2) spark post data
       should post to room and mention a user:
     AssertionError: expected messageRoom to have been called with arguments { channel: "#stackstorm", extra: undefined }, stanley: normal boring text
{ extra: undefined, id: "#stackstorm", name: "stanley", roomId: "#stackstorm" } { channel: "#stackstorm", extra: undefined } 
stanley: normal boring text
      at Context.<anonymous> (test/test-postdata.js:903:44)
  
  3) spark post data
       should post to room and not mention a user:
     AssertionError: expected messageRoom to have been called with arguments { channel: "#stackstorm", extra: undefined }, normal boring text
{ extra: undefined, id: "#stackstorm", name: undefined, roomId: "#stackstorm" } { channel: "#stackstorm", extra: undefined } 
normal boring text
      at Context.<anonymous> (test/test-postdata.js:923:44)
  
  4) spark post data
       should post to room with extra:
     AssertionError: expected messageRoom to have been called with arguments { channel: "#stackstorm", extra: { custom1: "attribute1", custom2: "attribute2" } }, stanley: normal boring text
{
  extra: { custom1: "attribute1", custom2: "attribute2" },
  id: "#stackstorm",
  name: "stanley",
  roomId: "#stackstorm"
} { channel: "#stackstorm", extra: { custom1: "attribute1", custom2: "attribute2" } } 
stanley: normal boring text
      at Context.<anonymous> (test/test-postdata.js:948:44)
  
  5) spark post data
       should post message with pretext to room:
     AssertionError: expected messageRoom to have been called with arguments { channel: "#stackstorm", extra: undefined }, stanley: NORMAL PRETEXT
normal boring text
{ extra: undefined, id: "#stackstorm", name: "stanley", roomId: "#stackstorm" } { channel: "#stackstorm", extra: undefined } 
stanley: NORMAL PRETEXT
normal boring text
      at Context.<anonymous> (test/test-postdata.js:993:44)


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The command "npm test" exited with 0.
store build cache

Done. Your build exited with 0.

This is due to a bug that has been reported multiple times to mocha:

• mocha 4 doesn't exit unlike mocha 3 mochajs/mocha#3044 - mocha 4 doesn't exit unlike mocha 3
• 🚀 Feature: Add option to exit with standard exit codes mochajs/mocha#3559 - Use standard exit codes
• Mocha exits with 0 exit code with failing tests mochajs/mocha#3893 - Mocha exits with 0 exit code with failing tests

This PR fixes this by passing the --exit flag to mocha. The first commit properly fails the Travis CI tests, and the second commit fixes the tests to match the changes in PR #200, which were tested against a real instance of Cisco Spark/Webex.

Using the --exit flag isn't exactly meant to solve this problem, but it does.