Install JavaScript dependencies during setup

In order to execute the webpacker:install command executed during the project’s rails new command execution, the development environment required a semi-current version of NodeJS available on the system.

The ASDF Version Manager is a useful tool that manages versions of system-level dependencies, like Ruby and NodeJS.

To integrate with ASDF, this commit declares a .tool-versions file that specifies the NodeJS version to be 11.7.0.

The rails new command that generated this project also generated a yarn install line in the project’s bin/setup script that is initially commented out.

To ensure that JavaScript dependencies are available to the development environment, this commit uncomments that line in the bin/setup script to also run yarn install when installing the application’s dependencies.