isogram: update tests to v1.7.0 (#1606)
isogram: update tests to v1.7.0 (#1606)

Closes #1586 
N-Parsons/exercism-python,exercism/python,jmluy/xpython,exercism/xpython,exercism/python,behrtam/xpython,smalley/python,smalley/python,exercism/xpython,jmluy/xpython,behrtam/xpython,N-Parsons/exercism-python