[hotfix] Ignore Hugo Module files

[MartijnVisser]

What is the purpose of the change

• Make sure that Hugo Modules files (which can be created while working on the current master branch) will be ignored when working with the currently support release-1.15 and release-1.14 branches

Brief change log

• Updated .gitignore

Verifying this change

This change is a trivial rework / code cleanup without any test coverage.

Does this pull request potentially affect one of the following parts:

• Dependencies (does it add or upgrade a dependency): no
• The public API, i.e., is any changed class annotated with @Public(Evolving): no
• The serializers: no
• The runtime per-record code paths (performance sensitive): no
• Anything that affects deployment or recovery: JobManager (and its components), Checkpointing, Kubernetes/Yarn, ZooKeeper: no
• The S3 file system connector: no

Documentation

• Does this pull request introduce a new feature? no
• If yes, how is the feature documented? not applicable

[flinkbot]

CI report:

• 83dca21 Azure: SUCCESS

Bot commands

The @flinkbot bot supports the following commands:

• @flinkbot run azure re-run the last Azure build

[zentol]

maybe remove leading slash (because it's a bit weird even if it works...)

[MartijnVisser]

maybe remove leading slash (because it's a bit weird even if it works...)

We also have those in for other ignores in the docs folder:

/docs/api
/docs/.bundle
/docs/.rubydeps
/docs/ruby2/.bundle
/docs/ruby2/.rubydeps
/docs/.jekyll-metadata

[zentol]

I saw that; it's still weird :P

[MartijnVisser]

I saw that; it's still weird :P

OK, fixed them all in one go