update nzshm-common to tagged release

[chrisdicaprio]

As developers, we have updated the the nzshm-common dependency in this library to a github branch, rather than a released version available on pypi. This was done to access a new feature in nzhsm-common in https://github.com/GNS-Science/TS1170.5-SDP that is not yet available in a release (mapping of Māori place names) (THS1170.5-SDP depends on toshi-hazard-store).

We need to revert the nzshm-common dependency back to a pypi release as soon as possible.

1. release nzhsm-common v0.8.4 (release v0.8.4 nzshm-common-py#58)
2. update THS nzshm-common dependency to use the pypi release