Fix simple typo: previousely -> previously

[timgates42]

Issue Type

[x] Bug (Typo)

Steps to Replicate

1. Examine README.md, README.rst.
2. Search for previousely.

Expected Behaviour

1. Should read previously.

Semi-automated issue generated by https://github.com/timgates42/meticulous/blob/master/docs/NOTE.md

To avoid wasting CI processing resources a branch with the fix has been prepared but a pull request has not yet been created. A pull request fixing the issue can be prepared from the link below, feel free to create it or request @timgates42 create the PR. Alternatively if the fix is undesired please close the issue with a small comment about the reasoning.

https://github.com/timgates42/stackimpact-python/pull/new/bugfix_typo_previously

Thanks.