hub api url generation fixes

Update Cucumber and Aruba test runners

This replaces Aruba's usage of ChildProcess with `popen3`. It supports
no process timeouts, but damn it's fast.

https://travis-ci.org/github/hub/jobs/574964882

No idea how this was suddenly broken! :/

Attempts to address intermittent "Rack application timed out during boot"
https://travis-ci.org/github/hub/jobs/574770004

Change quotes in Sync command to be consistent with Git style

Fixes #2233.

Remove NC/Nc from pr list formatting

Tweak Makefile to support older Go versions' backported module support

Fix error message on hub --paginate

README: Replace "Linuxbrew" with "Homebrew on macOS or Linux"

Avoid unnecessary conversions

Trap syscall.SIGTERM instead of os.Kill

Fixed ineffectual assignments in tests

Simplify code

Calling hub with one or more options but no subcommand resulted in the
following error message trying to expand an empty string as an alias:

	error: key does not contain variable name: alias.

This fixes the root cause: attempting to retrieve an invalid config key.

- We're (slowly) moving away from the Linuxbrew name, now Linux is
  officially supported.