robotstxt.info.yml should not contain "version: VERSION"

Since .info.yml contain "version: VERSION", such VERSION will be replaced by corresponding Drupal core version number. Therefore if install with git checkout, Available Update page will report that coming with an unsupported version number.

Documentation for Drupal 7.x (https://www.drupal.org/node/542202#version):

version (Discouraged)
The version string will be added by drupal.org when a release is created and a tarball packaged. However, if your module is not being hosted on the drupal.org infrastructure, you can give your module whatever version string makes sense (eg. see Release naming conventions).

Documentation for Drupal 8.x (https://www.drupal.org/node/2000204#hello_world):

For modules hosted on drupal.org, the version number will be filled in by the packaging script, you should not specify it manually, but leave out the version line entirely.