fix: fix golangci lint and travis

[gssbzn]

Description

golangci-lint should not be installed from source, their docs advice against it , this seems to be failing already on travis on a separate PR

I'm also fixing some linting errors flagged now by the tool

And also simplifying how travis is configured, some of the travis fixes I'm bringing them from the go client repo

Type of change:

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update
• Documentation fix/enhancement

Required Checklist:

• I have signed the MongoDB CLA
• I have read the Terraform contribution guidelines
• I have added tests that prove my fix is effective or that my feature works per HashiCorp requirments
• I have added any necessary documentation (if appropriate)
• I have run make fmt and formatted my code

Further comments

Some linting errors where flagged around how some regex could be simplified, I'm relaying on unit testing of the functions to catch a the regex from breaking

[gssbzn]

this is to allow your tests to run docker not to run the tests in docker so there's no point to enable it

[PacoDw]

Nice! thank you so much 👍

[themantissa]

LGTM and very much appreciate the fixes!