Allows the user to specify the log format version when setting up `s3logging` on the fastly service resource.
Requires an update to the vendored `go-fastly` dependency.
Also adds an additional acceptance test for the new attribute.
```
$ make testacc TEST=./builtin/providers/fastly TESTARGS='-run=TestAccFastlyServiceV1_s3logging'
==> Checking that code complies with gofmt requirements...
go generate $(go list ./... | grep -v /terraform/vendor/)
2017/02/06 14:51:55 Generated command/internal_plugin_list.go
TF_ACC=1 go test ./builtin/providers/fastly -v -run=TestAccFastlyServiceV1_s3logging -timeout 120m
=== RUN TestAccFastlyServiceV1_s3logging_basic
--- PASS: TestAccFastlyServiceV1_s3logging_basic (36.11s)
=== RUN TestAccFastlyServiceV1_s3logging_s3_env
--- PASS: TestAccFastlyServiceV1_s3logging_s3_env (15.35s)
=== RUN TestAccFastlyServiceV1_s3logging_formatVersion
--- PASS: TestAccFastlyServiceV1_s3logging_formatVersion (15.71s)
PASS
ok github.com/hashicorp/terraform/builtin/providers/fastly 67.186s
```
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