crystal: update to 0.27.2

[mohd-akram]

Description

Temporary patch is necessary as some tests fail due to an issue with libxml2 (see crystal-lang/crystal#7476).

Tested on

macOS 10.14.3 18D109
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?
• 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 #5616 Failed.

Lint results

--->  Verifying Portfile for crystal
--->  0 errors and 0 warnings found.

Port crystal success on xcode10.2. Log
Port crystal success on xcode9.4. Log
Port crystal fail on xcode7.3. Log

[yan12125]

Thank you for the update! As a side note, the libxml2 issue should be gone in the next libxml2 release - https://gitlab.gnome.org/GNOME/libxml2/commit/2c8dc7158a3b7b028454abcb6f162c4da28ed80b.