Fix `brew cask audit` not working without argument.

xcode: 8.3.1 is latest version.

missing_formula: fix undefined method `path` for nil:NilClass

formulary: Workaround for method missing for downcase on Pathname object

This check for a nil `tap` is necessary because Tap.from_path(path)
will simply return a nil value in the event the tap path is invalid

Our CI images are already updated with it.

gpg_spec test add 2.1.x compatibility

Virtualenv relocation fixes

Add probot-stale configuration.

Port audit_desc audit rules to a cop

audit: fix core formula alias check.

update-report: don't show new, installed formulae.

Was missing a formula object being passed.

These were those migrated from other taps but if they are installed
already: they aren't new to that user.

Revert "keg_relocate: Don't relocate dylib IDs containing metavariables."

Add Skylake to the Linux hardware list

java_requirement: Add newline to failure message

Signed-off-by: Bob W. Hogg <rwhogg@linux.com>

Xcode: update supported versions & download URLs for 8.3

Handle missing receipt on `brew install`.

For example if this is for a really old keg, keg where a user has
manually removed stuff or used `brew diy`.

ISSUE_TEMPLATE: tweak instructions.

Use `sudo` if parent path of `target` is not writable.

Be clearer about what's expected and where to file things.