Add lower bound on google-api-core, or google-cloud-core, or both

[drewbanin]

Describe the bug

From Slack:

Just upgraded to dbt=0.16.0 and got the following error message when running:
$ dbt run --models analytics_table
Running with dbt=0.16.0
Error importing adapter: No module named 'google.api_core.client_options'
Encountered an error:
No module named 'google.api_core.client_options'

It looks like client_options was added in 1.13.0, but the user above had v0.12.0 installed.

Let's check out the requirements of google-cloud-core and google-cloud-bigquery. I think we may need to bump the minimum version of google-cloud-core in order to support:

• client_options (via google-api-core)
• the timeout argument to api_request (also per Slack)

Users' env:

$ pip freeze | grep google
google-api-core==1.12.0
google-auth==1.11.3
google-cloud-bigquery==1.24.0
google-cloud-core==1.0.2
google-resumable-media==0.5.0
googleapis-common-protos==1.6.0

[beckjake]

Fixed in #2249