Add tflint 0.3.1

[hakamadare]

tflint is a Terraform linter.

After making all changes to the cask:

• brew cask audit --download {{cask_file}} is error-free.
• brew cask style --fix {{cask_file}} reports no offenses.
• The commit message includes the cask’s name and version.

Additionally, if adding a new cask:

• Named the cask according to the token reference.
• brew cask install {{cask_file}} worked successfully.
• brew cask uninstall {{cask_file}} worked successfully.
• Checked there are no open pull requests for the same cask.
• Checked the cask was not already refused in closed issues.
• Checked the cask is submitted to the correct repo.

[vitorgalvao]

This seems to be a CLI-only open-source tool. Please submit it first to Homebrew/core and only if they don’t accept it, submit here (linking back to the pull request where it was refused).

This policy is documented in faq/rejected_casks:

The app is both open-source and CLI-only (i.e. it only uses the binary artifact). In that case, and in the spirit of deduplication, submit it first to Homebrew/core. If it is rejected there, you may then try again in Homebrew-Cask (link us to the issue on Homebrew so we can see their reasoning for rejection).