Turn validation fixture into valid Json

Since the fixture for valid Json had a trailing comma, the fixture got
"json_decode"d to null for Zend (not HHVM), which trivially passed
validation.
We turn the fixture into valid Json, so the test is actually testing
schema validation with non-trivial array on Zend.

Change-Id: Icc9325c62569df4d1c5e827efd75f20af0c19e07