Move eslint-config-airbnb-base to devDependencies

An inappropriate command was used at the time of the addition of the eslint-config-airbnb-base dependency to the
project. Since this is used only for linting and is not needed by the distribution, an `npm install --save-dev` command
should have been used to add the dependency, which would have added it under the appropriate devDependencies key of
package.json. The omission of the `--save-dev` flag from the command caused it to instead be added under the
`dependencies` key.

The dependency is hereby classified appropriately for its use in the project.