[path_provider] Update the Linux example template

[robert-ancell]

Minor change, no issue opened.

Pre-launch Checklist

• I read the [Contributor Guide] and followed the process outlined there for submitting PRs.
• I read the [Tree Hygiene] wiki page, which explains my responsibilities.
• I read and followed the [Flutter Style Guide] and the [C++, Objective-C, Java style guides].
• I signed the [CLA].
• The title of the PR starts with the name of the plugin surrounded by square brackets, e.g. [shared_preferences]
• I listed at least one issue that this PR fixes in the description above.
• I updated pubspec.yaml with an appropriate new version according to the [pub versioning philosophy].
• I updated CHANGELOG.md to add a description of the change.
• I updated/added relevant documentation (doc comments with ///).
• I added new tests to check the change I am making or feature I am adding, or Hixie said the PR is test exempt.
• All existing and new tests are passing.

[stuartmorgan-g]

This isn't valid on the stable channel.

[stuartmorgan-g]

@robert-ancell Ping; is there a specific issue this was trying to solve? This should auto-migrate for people when building on master.

[robert-ancell]

This PR was just to test if the CI build failures were due to #3077. I thought this change was trivial but apparently not trivial enough :)

[stuartmorgan-g]

Closing for now; if there's a specific need to land something like this before the changes reach stable we'll need to figure out how to address that, but it should be fine to just wait AFAIK.