Part of the changes in 2591 modifies the vendor directory
which should not be modified. `dep ensure` will change it back.
This fix reverts the change of
```
vendor/github.com/apache/thrift/lib/go/thrift/simple_json_protocol.go
```
in 2591.
Signed-off-by: Yong Tang <yong.tang.github@outlook.com>
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