Fix the Travis configuration

exit should not be used in script commands, because it exits the whole build script.
Thus, turning a failure exit code into another failure exit code is not needed.

.travis.yml

@@ -21,7 +21,7 @@ before_script:
     - git config --global user.email travis@example.com
 
 script:
-    - ls -d tests/Composer/Test/* | parallel --gnu --keep-order 'echo "Running {} tests"; ./vendor/bin/phpunit -c tests/complete.phpunit.xml {};' || exit 1
+    - ls -d tests/Composer/Test/* | parallel --gnu --keep-order 'echo "Running {} tests"; ./vendor/bin/phpunit -c tests/complete.phpunit.xml {};'
 
 git:
-  depth: 5
+  depth: 5