Update coffee-script-source, sass, foreman

* foreman (0.75.0 > 0.74.0)
* guard-jekyll-plus (1.4.10 > 1.4.9)
* coffee-script-source (1.8.0 > 1.7.1)
* minitest (5.4.1 > 5.4.0)
* sass (3.4.2 > 3.4.1)