Support for Device Group's user-defined Environment Variables

Merge pull request #33 from electricimp/develop

Update version number to 1.7.0

1.5.0-ci-testing

• Added Team City badge
• Removed travis.yml
• Updated .gitignore

1.5.0

• Support for DuT device groups.

1.4.2

• support reconnections/retries for login-key commands

1.4.1

• tests excluded from npm package
• package.json dependencies versions updated

1.4.0

• Support region attribute for Device Group

1.3.1

• impt auth enhancements

1.3.0

• Support for 2FA and OTP in impt introduced.

1.2.0

• Introduced environment variables for proxy setup.

1.1.1

• testing section added to readme
• tests improved