[regression] Follow-up for #2995960 and #2992833: syntax errors in PHP 5.5 & 5.6

Same problem reproduced. Great.

Now let's fix it.

This regression was introduced in #2995960: Add a Link and LinkCollection class to support RFC8288 web linking..

Green on 5.6! Now also queueing a PHP 5.5 test, just to make sure.

Hah. #2992833: Add a version negotiation to revisionable resource types introduced a regression too. One caused by the nicer PHP syntax that \Drupal\jsonapi\JsonApiSpec::isValidMemberName() refrained from using precisely because PHP 5.6 is not yet a requirement.

✅ on 5.5, 5.6, 7.0. Let's do this.

Just one nit:

+++ b/src/Revisions/ResourceVersionRouteEnhancer.php
@@ -44,19 +44,19 @@ final class ResourceVersionRouteEnhancer implements EnhancerInterface {
+   * @todo When D8 requires PHP >=5.6, convert tot expression using the VersionNegotiator::SEPARATOR constant.

s/tot/to/

d.o, you're drunk.