composer.json needs update

composer.json has version "dev-master" for "satooshi/php-coveralls", and it will cause this error during install:
Problem 1
- The requested package satooshi/php-coveralls dev-master exists as satooshi/php-coveralls[0.1.0, 0.2.0, 0.3.0, 0.3.1, 0.3.2, 0.4.0, 0.5.0, 1.0.x-dev, 1.1.x-dev, 2.0.x-dev, v0.6.0, v0.6.1, v0.7.0, v0.7.1, v1.0.0, v1.0.1, v1.0.2, v1.1.0, v2.0.0] but these are rejected by your constraint.

Start with composer.json and inspect the satooshi/php-coveralls dependency constraint. Run the Composer install command that currently reports the rejection, update the constraint to a compatible released version, and rerun the install to confirm the error is gone.

Written by the indexing model from the issue text.