Show sandcastle URL in phabricator

Show sandcastle URL in phabricator

Summary:
We are passing a string as diff_id which make conduit call fail

```
$ echo '{"diff_id": "20982117", "name":"click here for sandcastle tests for D20982117", "link":"https://our.intern.facebook.com/intern/sandcastle/1984718793/"}' | arc call-conduit differential.updateunitresults
{"error":"ERR-CONDUIT-CORE","errorMessage":"ERR-CONDUIT-CORE: Argument 1 passed to EntDiffPropertiesUpdateMutationBuilder::setDiffNumber() must be an instance of int, string given","response":null}
```

fix it by removing double quotes
Closes https://github.com/facebook/rocksdb/pull/1700

Differential Revision: D4350227

Pulled By: IslamAbdelRahman

fbshipit-source-id: b4504af