Regression script cannot directly download files from GitHub, because it does not work for private repositories - we need to use GitHub's API to get the composer.json file.

Steps to reproduce:
1. Run regression script (bin/.travis/trigger_regression_build.sh
2. Enter one PR, for example: https://github.com/ezsystems/ezplatform-workflow/pull/112

Expected:
Script runs correctly, build is created

Actual:
See screenshot for error