Add support for the inferno eslint package - eslint-plugin-inferno.

Constrain the `eslint-plugin-inferno` plugin to 6.9.* (with the latest
matching version being 6.9.2). Starting with version 6.10.* of the
package, the peer dependencies have changed requiring `eslint@^3.16.1`.

Currently, the CodeClimate eslint package is installing 3.14.1.