Updates travis config to use locally installed phpunit.

Author: dsposito

.travis.yml

@@ -12,7 +12,7 @@ before_script:
 # Run tests and generate test coverage report.
 script:
   - vendor/bin/phpcs ./src ./tests --extensions=php --standard=PSR2
-  - phpunit -d api_key=$API_KEY --coverage-clover build/logs/clover.xml
+  - vendor/bin/phpunit -d api_key=$API_KEY --coverage-clover build/logs/clover.xml
 
 # Submit test coverage report to Coveralls.
 after_success: