Less files in plugin subfolder ignored

[swashbuck]

Subject of the issue

Less files in a plugin's less subfolder were not included when we are using build.includes in config.json. Discovered while working on this Media PR.

Your environment

• Framework

To reproduce

1. In config.json, only include the plugins you wish to use. One of them should have a subfolder in their less directory.

  "build": {
    "strictMode": true,
    "includes": [
      "adapt-plugin-with-less-subfolder",
      "adapt-contrib-text",
      "adapt-contrib-boxMenu",
      "adapt-contrib-vanilla"
    ]
  },

2. Build the course.