Build with golang 1.16

[travisn]

Is this a bug report or feature request?

• Feature Request

What should the feature do:
It's time to move to golang 1.16 in the builds as a requirement. The builds currently allow for either 1.15 or 1.16 for flexibility while 1.16 was recently out, but now we need to take advantage of 1.16 for issues such as #7609 and #7913.

This should be as simple as:

• Update the github actions to use golang 1.16
• Set the required build version to 1.16

What is use case behind this feature:
Build with updated features and dependencies.