Add PHP7 support to travisci config.

[tw2113]

As per ​https://github.com/travis-ci/travis-ci/issues/2480#issuecomment-75988205, TravisCI now supports testing against PHP7.

This patch will add 7 to the list of supported versions to test against.

[DJPaul]

Some Slackchat here ​https://wordpress.slack.com/archives/buddypress/p1424884467002986

[DJPaul]

Make it like this ​https://buddypress.trac.wordpress.org/changeset/8392/trunk/.travis.yml so PHP 7 tests can fail without failing the whole suite, just in case PHP 7 turns out to have issues.

[tw2113]

Will amend and re-submit, thanks for the feedback :)

[tw2113]

Updated to allow failure for the 7/nightly build, and added a trailing .0 so that we can have more assured version checking in the future.

[netweb]

Related: ​#WP31454

The 7 / 7.0 is an alias of nightly, I think we should use as WordPress Core plans and use nightly rather than 7/7.0.

Once PHP 7 is released then adding as a PHP version 7.0 to the build matrix and retaining the "allowed to fail" nightly would be the way to go.

Travis CI Docs reference: ​http://docs.travis-ci.com/user/languages/php/#PHP-nightly-builds

[tw2113]

As per Stephen's feedback and copying his bbPress patch as best I could, revision 3 attempt :)

[netweb]

Replying to tw2113:

As per Stephen's feedback and copying his bbPress patch as best I could, revision 3 attempt :)

Perfect :)

Reference:

• Build ​https://travis-ci.org/ntwb/BuddyPress/builds/52231435
• Job ​https://travis-ci.org/ntwb/BuddyPress/jobs/52231466

[boonebgorges]

In 9560:

Add PHP nightly build as an allowed failure in Travis CI test matrix.

Props tw2113, netweb.
Fixes #6256.