isogram: updates tests to v1.6.0 (#1499)
isogram: updates tests to v1.6.0 (#1499)

New to this project, but noticed this test was out-of-date. Modified it to match new test suite.
behrtam/xpython,behrtam/xpython,jmluy/xpython,N-Parsons/exercism-python,jmluy/xpython,N-Parsons/exercism-python,smalley/python,exercism/python,exercism/xpython,smalley/python,exercism/xpython,exercism/python