chore(python): simplify nox steps in CONTRIBUTING.rst (#133)

Source-Link: googleapis/synthtool@26558ba Post-Processor: gcr.io/repo-automation-bots/owlbot-python:latest@sha256:99d90d097e4a4710cc8658ee0b5b963f4426d0e424819787c3ac1405c9a26719

Author: gcf-owl-bot[bot]

.github/.OwlBot.lock.yaml

@@ -1,3 +1,3 @@
 docker:
  image: gcr.io/repo-automation-bots/owlbot-python:latest
- digest: sha256:df50e8d462f86d6bcb42f27ecad55bb12c404f1c65de9c6fe4c4d25120080bd6
+ digest: sha256:99d90d097e4a4710cc8658ee0b5b963f4426d0e424819787c3ac1405c9a26719

CONTRIBUTING.rst

@@ -68,14 +68,12 @@ Using ``nox``
 We use `nox <https://nox.readthedocs.io/en/latest/>`__ to instrument our tests.
 
 - To test your changes, run unit tests with ``nox``::
+ $ nox -s unit
 
- $ nox -s unit-3.8
- $ ...
+- To run a single unit test::
 
-- Args to pytest can be passed through the nox command separated by a `--`. For
- example, to run a single test::
+ $ nox -s unit-3.9 -- -k <name of test>
 
- $ nox -s unit-3.8 -- -k <name of test>
 
  .. note::
 
@@ -142,7 +140,7 @@ Running System Tests
 - To run system tests, you can execute::
 
  # Run all system tests
- $ nox -s system-3.8
+ $ nox -s system
 
  # Run a single system test
  $ nox -s system-3.8 -- -k <name of test>
@@ -215,8 +213,8 @@ Supported versions can be found in our ``noxfile.py`` `config`_.
 .. _config: https://github.com/googleapis/python-iot/blob/master/noxfile.py
 
 
-We also explicitly decided to support Python 3 beginning with version
-3.6. Reasons for this include:
+We also explicitly decided to support Python 3 beginning with version 3.6.
+Reasons for this include:
 
 - Encouraging use of newest versions of Python 3
 - Taking the lead of `prominent`_ open-source `projects`_