REGEX not matching all composer versions

[killkelleyr]

In which file did you encounter the issue?

File: composer/tools/composer_dags.py

Did you change the file? If so, how?

No

Describe the issue

The current regex expression does not work for environment versions that do not include minor and or patch

Error

Traceback (most recent call last):
  File "/home/rkillkelley/composer_dags.py", line 229, in <module>
    main(
  File "/home/rkillkelley/composer_dags.py", line 168, in main
    ).groups()
AttributeError: 'NoneType' object has no attribute 'groups'