Remove hard coding of PYGEOAPI_VERSION_TAG
In MR #91, one of the changes we had to make to re-deploy was hard-coding PYGEOAPI_VERSION_TAG
as 0.16.dev0+limno.1-beta
, because using the Github API to access the latest release was failing. Hard-coding the release is a fine short-term fix, but we should come up with a better strategy for defining this variable.