minor symfony#15164 Move HHVM tests out of the allowed failures (nicolas-grekas)

This PR was merged into the 2.3 branch.

Discussion
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Move HHVM tests out of the allowed failures

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | -
| License       | MIT
| Doc PR        | -

2.3, 2.6 and 2.7 are now green on HHVM, let's ensure this remains always true!

Commits
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ff2ead1 Move HHVM tests out of the allowed failures

Author: fabpot

.travis.yml

@@ -22,7 +22,6 @@ matrix:
         - php: hhvm
     allow_failures:
         - php: nightly
-        - php: hhvm
     fast_finish: true
 
 services: mongodb