api streamTransactions unit test failure

[tonyz-defi]

unit test fails because current knowledgr chain has no transactions.
We need to comment this for now, and remove comment later.

     AssertionError: expected undefined to exist
      at test/api.test.js:104:18
      at src/api/index.js:281:17
      at src/api/index.js:258:17
      at src/api/index.js:234:21
      at tryCatcher (node_modules/bluebird/js/release/util.js:16:23)
      at Promise._settlePromiseFromHandler (node_modules/bluebird/js/release/promise.js:512:31)
      at Promise._settlePromise (node_modules/bluebird/js/release/promise.js:569:18)
      at Promise._settlePromise0 (node_modules/bluebird/js/release/promise.js:614:10)
      at Promise._settlePromises (node_modules/bluebird/js/release/promise.js:689:18)
      at Async._drainQueue (node_modules/bluebird/js/release/async.js:133:16)
      at Async._drainQueues (node_modules/bluebird/js/release/async.js:143:10)
      at Immediate.Async.drainQueues [as _onImmediate] (node_modules/bluebird/js/release/async.js:17:14)