shellcheck: Update to 0.7.0

[neverpanic]

Description

Closes: https://trac.macports.org/ticket/58121
Closes: https://trac.macports.org/ticket/51568

Type(s)

• bugfix
• enhancement
• security fix

Tested on

macOS 10.13.6 17G8030
Xcode 10.1 10B61

Verification

Have you

• followed our Commit Message Guidelines?
• squashed and minimized your commits?
• checked that there aren't other open pull requests for the same change?
• referenced existing tickets on Trac with full URL?

• checked your Portfile with port lint?
• tried existing tests with sudo port test?
• tried a full install with sudo port -vst install?
• tested basic functionality of all binary files?

[macportsbot]

Travis Build #7948 Passed.

Lint results

--->  Verifying Portfile for shellcheck
Error: Line 2 has unrecognized PortGroup
--->  1 errors and 0 warnings found.

Port shellcheck success on xcode10.3. Log
Port shellcheck success on xcode9.4. Log
Port shellcheck success on xcode8.3. Log