Typo in doc

[zhongjiajie]

For general questions:

I just find typo in documentation
In https://github.com/oracle/python-cx_Oracle/blob/master/doc/src/module.rst
L192 availablity -> availability

[zhongjiajie]

@anthony-tuininga , PTAL, thx

[anthony-tuininga]

Yep. Typo. Thanks!