title: LiveDataReactiveStreams.fromPublisher is not working
body: <p>I am trying to create a <code>LiveData</code> object from an RxJava2 <code>Observable</code> using <code>LiveDataReactiveStreams.fromPublisher</code>. However, while the LiveData object is being created (from my ViewModel), it never fires when being observed (from my Fragment).</p>
  
  <p>Here's a basic example. For comparison, I have included the alternative way of getting this data from an Observable into LiveData (by subscribing to the Observable).</p>
  
  <pre><code>class MainFragmentViewModel : ViewModel() {
  
      val liveData1: LiveData&lt;List&lt;Int&gt;&gt;
      val liveData2: MutableLiveData&lt;List&lt;Int&gt;&gt; = MutableLiveData()
  
      private val disposeBag = CompositeDisposable()
  
      init {
          val obs: Observable&lt;List&lt;Int&gt;&gt; = Observable.just(listOf(1, 2, 3))
  
          liveData1 = LiveDataReactiveStreams.fromPublisher { obs }
  
          obs.subscribe { liveData2.value = it }.addTo(disposeBag)
      }
  }
  </code></pre>
  
  <pre><code>class MainFragment : Fragment() {
  
      private val vm: MainFragmentViewModel by viewModel()
  
      override fun onStart() {
          super.onStart()
  
          vm.liveData1.observe(viewLifecycleOwner, Observer {
              Timber.d("The liveData1 list has count ${it.count()}")
          })
          vm.liveData2.observe(viewLifecycleOwner, Observer {
              Timber.d("The liveData2 list has count ${it.count()}")
          })
      }
  }
  </code></pre>
  
  <p>Logcat now contains only this:</p>
  
  <p><code>D/MainFragment$onStart: The liveData2 list has count 3</code></p>
  
  <p>In other words, using <code>LiveDataReactiveStreams.fromPublisher</code> doesn't do anything, while subscribing to the Observable directly and updating the <code>LiveData</code>'s value works fine. What am I doing wrong?</p>