Error parsing hng6

[Keith-Hon]

Describe the bug A clear and concise description of what the bug is. Error thrown when calling pycantonese.parse_jyutping('hng6')

To reproduce Steps to reproduce the behavior, including the complete stack trace if possible: pycantonese.parse_jyutping('hng6')

Expected behavior A clear and concise description of what you expected to happen instead. Should return [Jyutping(onset='h', nucleus='ng', coda='', tone='6')]

Screenshots If applicable, add screenshots to help explain your problem.

System (please complete the following information):

• Operating System: [e.g. Windows, MacOS, Linux]
• PyCantonese version: [What you see after you run import pycantonese; print(pycantonese.__version__)]

Additional context Add any other context about the problem here.

[Keith-Hon]

https://github.com/Keith-Hon/pycantonese/commit/241b5215feb29651cef107321485233b0d3fa63e

[yuzuda283]

same error on version 3.4