Travis CI: use folding to group checks results

[php-coder]

This also means that we don't need to save the commands output to files and print it later, now Travis might show their output in live.

See for details: travis-ci/docs-travis-ci-com#949

[php-coder]

This also means that we don't need to save the commands output to files and print it later, now Travis might show their output in live.

We still need to write output into files because now we shows a brief statistic on the top, before the output of the commands. Also, buffering to a file gives us ability to filter out useless "Downloading " messages from Maven.

[php-coder]

There is an open branch for that: https://github.com/php-coder/mystamps/tree/gh1085_travis_folding

[php-coder]

In light of migration to GitHub Actions (#1154), this change isn't needed.