Fix Python 2.7 syntax

[gonzalocasas]

Pull Request https://github.com/gramaziokohler/roslibpy/pull/105 introduced syntax that is not compatible with Python 2.7 / IronPython.

What type of change is this?

• [x] Bug fix in a backwards-compatible manner.
• [ ] New feature in a backwards-compatible manner.
• [ ] Breaking change: bug fix or new feature that involve incompatible API changes.
• [ ] Other (e.g. doc update, configuration, etc)

Checklist

Put an x in the boxes that apply. You can also fill these out after creating the PR. If you're unsure about any of them, don't hesitate to ask. We're here to help! This is simply a reminder of what we are going to look for before merging your code.

• [x] I added a line to the CHANGELOG.rst file in the Unreleased section under the most fitting heading (e.g. Added, Changed, Removed).
• [x] I ran all tests on my computer and it's all green (i.e. invoke test).
• [x] I ran lint on my computer and there are no errors (i.e. invoke check).
• [ ] I have added tests that prove my fix is effective or that my feature works.
• [ ] I have added necessary documentation (if appropriate)

[gonzalocasas]

/cc @DomenicP

[DomenicP]

Apologies for introducing this bug, didn't realize that TimeoutError was new in Python 3. It looks like this repo is already setup with GitHub Actions and a matrix for Python versions, maybe it would be helpful to add all of the Python versions for actively supported ROS distros or Python versions to that matrix? I'll look into opening a follow-up PR to add this

[DomenicP]

Opened #107 if anyone is interested in a follow-up discussion for testing compatibility with Python 2.7 (and other Python 3 versions).