CHANGELOG updates
Copy cmd.Env fron os.Environ() to inherit from the OS environment. Fixes #142.
Merge pull request #143 from mcroydon/event-handler-environment

Copy cmd.Env fron os.Environ() to inherit from the OS environment. Fixes...
Make sure that event handlers pass through environment variables.
Merge pull request #144 from mcroydon/event-handler-environment

agent: Make sure that event handlers pass through environment variables.
Merge pull request #5 from hashicorp/master

Merge Mainline