Update chaneglog for 0.8.1
Update chaneglog for 0.8.1

dart-lang/dartdoc,astashov/dartdoc,dart-lang/dartdoc,astashov/dartdoc,keertip/dartdoc,keertip/dartdoc,astashov/dartdoc,keertip/dartdoc,dart-lang/dartdoc,keertip/dartdoc,astashov/dartdoc,dart-lang/dartdoc