Fix jest deprecation warning.

Test Plan:
- With freshly installed npm modules,
- Verify "testResultsProcessor support is deprecated" is no longer
  displayed when running jest tests locally.
- Open the jenkins job from this PS.
- Go to the test report > (root)
- Verify "Free-form Rubric with a custom criterion by default renders
  the root component as expected" is present in the report

Change-Id: I921138e2a9a1025a3ed665693a6223819bf76392
Reviewed-on: https://gerrit.instructure.com/156778
Reviewed-by: Clay Diffrient <cdiffrient@instructure.com>
Tested-by: Jenkins
Product-Review: Neil Gupta <ngupta@instructure.com>
QA-Review: Neil Gupta <ngupta@instructure.com>

jest.config.js

@@ -10,6 +10,7 @@ module.exports = {
     'public/javascripts',
     'public/javascripts/vendor'
   ],
+  reporters: [ "default", "jest-junit" ],
   setupFiles: [
     'jest-localstorage-mock',
     '<rootDir>/jest/jest-setup.js'
@@ -17,7 +18,6 @@ module.exports = {
   testMatch: [
     '**/__tests__/**/?(*.)(spec|test).js'
   ],
-  testResultsProcessor: 'jest-junit',
   transform: {
     '^i18n': '<rootDir>/jest/i18nTransformer.js',
     '^.+\\.jsx?$': 'babel-jest'