Set 'typing' package to be installed only on Python 2.7. This fixes the import issue raised in Python 3.7 and 3.8 on using the 'typing' module.

Issue report here with complete information

Type of changes

• Bug fix
• New feature
• Documentation / docstrings
• Tests
• Other

Checklist

• I've run the latest black with default args on new code.
• I've updated CHANGELOG.md and CONTRIBUTORS.md where appropriate.
• I've added tests for new code.
• I accept that @willmcgugan may be pedantic in the code review.

Description

Please describe your changes here. If this fixes a bug, please link to the issue, if possible.