Update absinthe to 1.5

[johnshaughnessy]

Update absinthe to 1.5 with mix update absinthe and some changes to mix.exs. I want to do this update first before continuing development of the API (e.g. Set up telemetry) (See Hubs-Foundation/hubs-cloud#154).

Upgraded:
  absinthe 1.4.16 => 1.5.5
  absinthe_phoenix 1.4.4 => 1.5.0
  absinthe_plug 1.4.7 => 1.5.3
  mime 1.4.0 => 1.5.0
  phoenix_html 2.14.1 => 2.14.3
  plug 1.10.4 => 1.11.0
  plug_crypto 1.1.2 => 1.2.0
New:
  nimble_parsec 1.1.0

Updates made to the mix.exs file are explained below:

Update elixir version in mix.exs because:

• Hubs Cloud environments are configured to use elixir 1.8.0 (https://github.com/mozilla/reticulum/blob/4630a3dce2a12a48ddd382e3a1385cdcc83d3456/habitat/plan.sh#L19)
• absinthe requires elixir 1.8 (https://github.com/absinthe-graphql/absinthe/#installation)

Update absinthe to 1.5 so that we get

• built-in telemetry instrumentation
• lower subscription memory usage
• bug fixes
  Changelog: https://github.com/absinthe-graphql/absinthe/blob/master/CHANGELOG.md#changelog
  If we want to update absinthe to 1.6, I think we have to update to absinthe_phoenix to 2.0, which requires phoenix 1.5+ .

Update absinthe_plug to 1.5 because it is required for absinthe 1.5+
Changelog: https://github.com/absinthe-graphql/absinthe_plug/blob/master/CHANGELOG.md

Update absinthe_phoenix to 1.5 because it is required for absinthe 1.5+
Changelog: https://github.com/absinthe-graphql/absinthe_phoenix/blob/master/CHANGELOG.md#v150
Phoenix 1.4 version info: https://github.com/absinthe-graphql/absinthe_phoenix/tree/v1.5
Phoenix 1.5 info: https://github.com/absinthe-graphql/absinthe_phoenix#phoenix-15

[johnshaughnessy]

closing this in favor of closing this in favor of #460