Update composer example installation to a more recent version of the Chosen library

Problem/Motivation

The README.txt provides an example composer installation for the Chosen library:

"repositories": [
    {
      "type": "package",
      "package": {
        "name": "harvesthq/chosen",
        "version": "1.6.1",
        "type": "drupal-library",
        "dist": {
          "url": "https://github.com/harvesthq/chosen/releases/download/v1.6.1/chosen_v1.6.1.zip",
          "type": "zip"
        },
        "require": {
            "composer/installers": "^1.2.0"
        }
      }
    }
  ]

This example works fine, but version 1.6.1 of Chosen was release little over a year ago.

Proposed resolution

Let's update this to a more recent release, for example the current 1.7.0: https://github.com/harvesthq/chosen/releases

Remaining tasks

1. Write a patch
2. Review
3. Commit

User interface changes

None.

API changes

None.

Data model changes

None.