After 866da19fd9 we now use package.json
to install Action Text's JS dependencies (see JS_PACKAGE_PATH).
But when the gem pacakge for Action Text is built, package.json was not
included so running `rails action_text:install` in a Rails app would
fail with:
```
rails action_text:install
rails aborted!
Errno::ENOENT: No such file or directory @ rb_sysopen - xxx/gems/actiontext-6.0.0.alpha/lib/templates/../../package.json
./bin/rails:4:in `<main>'
Tasks: TOP => app:template
(See full trace by running task with --trace)
```
This comment was autogenerated, see
`railties/lib/rails/generators/rails/plugin/templates/%name%.gemspec.tt`
Since actiontext is well described in this file, I think we shouldn't
keep this comment. Note that this commit is more like cosmetic change,
so it is OK if we don't merge this.
