feat: Run tests for sub packages in CI (#374)

Summary:

Travis CI Only run tests for optimizely-sdk package. This PR makes Travis CI run unit tests for other sub packages on node 12

Test Plan:

Tested on Travis CI

Author: zashraf1985

.travis.yml

@@ -31,6 +31,7 @@ stages:
   - 'Benchmarking tests'
   - 'Cross-browser and umd unit tests'
   - 'Test'
+  - 'Test sub packages'
 
 jobs:
   include:
@@ -56,3 +57,13 @@ jobs:
     - stage: Cross-browser and umd unit tests
       node_js: '8'
       script: npm run test-ci
+    - &packagetest
+      stage: 'Test sub packages'
+      node_js: '12'
+      before_install: cd packages/datafile-manager
+    - <<: *packagetest
+      before_install: cd packages/event-processor
+    - <<: *packagetest
+      before_install: cd packages/logging
+    - <<: *packagetest
+      before_install: cd packages/utils