Improve plist handling for `hdiutil` commands

- Raise `CaskError` instead of `Plist::ParseError` from module
- Improve error message when parse result is empty
- remove leading garbage text and emit it to stderr (seen in #5060)
- remove trailing garbage text and emit it to stderr (seen in #4819)

This has the incidental effect of emitting DMG licenses during
installation, which seems desirable as permanent functionality.

If not permanent, the warnings to STDERR should still be kept
temporarily to help get better bug reports on `hdiutil`.

A bug wrt DMG licenses must have been introduced in one of
#4892, #4887, #4889, #4900, #4975, #4978, or #4857.  Presumably,
the cause is that STDERR was previously silenced when running
`hdiutil`.  It would be cleaner (and more reliable) to redirect
STDERR and examine it separately, rather than clean up the
merged outputs.

closes #4819
closes #5060
new forced seed for Travis

As predicted in #5037, the codebase drifted, and the old forced
seed started failing consistently on Ruby 2.x builds.
Merge pull request #5064 from rolandwalker/update_travis_seed

new forced seed for Travis
Update minimal clock cask to use package installer

Minimal Clock screensaver changed to a package installer, so update the
Cask accordingly and with @rolandwalker help.

Issue: #4989
Merge pull request #5068 from chrisopedia/update-minimalclock

Update minimal clock cask to use package installer
Update blink1control cask to v1.82

Closes #5070
Merge pull request #5063 from rolandwalker/hdiutil_plist_handling

Improve plist handling for `hdiutil` commands
cut v0.37.1
fix missing changelog entries for 0.37.1
Add MacDown 0.1
Merge pull request #5071 from Ephemera/macdown

Add MacDown 0.1
Comment on non-Sparkle appcast

See Issue #5057
iExplorer 3.3.2.0

Closes #5073
MacUpdate Desktop 6.0; suppress move to /Applications alert

Closes #5072
Add ForkLift version 2.6.1
Update to Dogecoin-Qt 1.7
Merge pull request #5075 from hanxue/epubtopdf-appcast

Comment on non-Sparkle appcast
Merge pull request #5079 from Fapper/patch-1

Update to Dogecoin-Qt 1.7
Merge pull request #5077 from vinkla/forklift

Add ForkLift version 2.6.1
Fixed sha256 to match 1.7.1 release.

Closes #5081