Add Hashicorp terraform CLI to "arkade get" and --version override to all "get" commands.

Changelog for 0.6.10:

• PR #201 Add terraform CLI by @alexellis
• PR #197 Remove helm template by @amalkh5

Usage:

# Stable version 0.13.0
arkade get terraform

# Get an older version
arkade get terraform --version 0.12.0

Commits
08ce44c Add terraform CLI by @alexellis
653c4b3 add helm3 support to chart,cronconnector, by @amalkh5

Generated by Derek