Fix runtime warning on Figure calls

[ljvmiranda921]

Resolves #65

[ljvmiranda921]

Test this properly, don't just merge

• https://medium.com/zendesk-engineering/hunting-for-memory-leaks-in-python-applications-6824d0518774
• https://medium.com/python-features/understanding-memory-usage-and-leaks-in-our-python-code-beginners-c9dc211887af
• http://tech.labs.oliverwyman.com/blog/2008/11/14/tracing-python-memory-leaks/
• https://code.activestate.com/recipes/65333/

[ljvmiranda921]

https://abalkin.github.io/pytest-leaks/#usage