Fix composer scripts

[piotr-cz]

When trying to run composer scripts, instead of executing their file is printed on screen.
For example

composer phpunit
> php vendor/bin/phpunit

dir=$(cd "${0%[/\\]*}" > /dev/null; cd "../phpunit/phpunit" && pwd)

if [ -d /proc/cygdrive ]; then
    case $(which php) in
        $(readlink -n /proc/cygdrive)/*)
            # We are in Cygwin using Windows php, so the path must be translated
            dir=$(cygpath -m "$dir");
            ;;
    esac
fi

"${dir}/phpunit" "$@"

Fixed by adjusting to suggestions:

• Composer > Scripts > Writing custom commands
• changed phpstan arguments to suggested here

[coveralls]

Coverage remained the same at 100.0% when pulling 87a1c45 on piotr-cz:bugfix/composer-scripts into 62b7295 on slimphp:4.x.

[l0gicgate]

We should probably fix that on all the repos @adriansuter

[adriansuter]

@l0gicgate Yes, we should.