Update circleci to go version 1.13 and fix associated errors

[Scott Barnard]

Circleci uses go version 1.12 for building and testing. Using go 1.13 causes some tests to fail, so there are some errors that need fixing.

[Alan Noble]

Resolved in https://bitbucket.org/ausocean/iot/commits/8290ed236f85cb8ae42e9e751d5820f8e47dfb6e