Don't display error message that is helpful during testing in production environment

[rjkip]

When QA Tools is running in verbose mode, and Composer installation fails, the following, highlighted in red, is included in the error message that is displayed. This message is relevant and helpful during testing, but irrelevant and confusing in production.

   * Installing Composer development dependencies...
  [error] Failed to require development dependencies
  One of these packages could not be installed (from inside /home/rjkip/Projects/qa-tools/):
   - phpunit/phpunit:^5.7
   - jakub-onderka/php-parallel-lint:^0.9.2
   - phpmd/phpmd:^2.0
   - squizlabs/php_codesniffer:^2.7
   - sensiolabs/security-checker:^3.0
- Maybe you forgot to:
-  - add a composer.json fixture for the package to 'tests/composer/packages'
-  - add the package to '\Ibuildings\QaTools\SystemTest\Composer::initialise'