Baselines for Tensorflow 2.0. (#978)

* Baselines for Tensorflow 2.0.

Please do note that:
1. ACER, ACKTR, GAIL is still under development by external
contributors.
2. HER is still under development by tanzheny@google.com.

* Some cleanup.

* Addressing some comments.

setup.py

@@ -12,9 +12,10 @@ extras = {
         'filelock',
         'pytest',
         'pytest-forked',
-        'atari-py',
-        'matplotlib',
-        'pandas'
+        'atari-py'
+    ],
+    'bullet': [
+        'pybullet',
     ],
     'mpi': [
         'mpi4py'
@@ -31,10 +32,13 @@ setup(name='baselines',
       packages=[package for package in find_packages()
                 if package.startswith('baselines')],
       install_requires=[
-          'gym>=0.10.0, <1.0.0',
+          'tf-nightly-2.0-preview',
+          'gym',
           'scipy',
           'tqdm',
           'joblib',
+          'dill',
+          'progressbar2',
           'cloudpickle',
           'click',
           'opencv-python'
@@ -44,17 +48,5 @@ setup(name='baselines',
       author='OpenAI',
       url='https://github.com/openai/baselines',
       author_email='gym@openai.com',
-      version='0.1.6')
+      version='0.1.5')
 
-
-# ensure there is some tensorflow build with version above 1.4
-import pkg_resources
-tf_pkg = None
-for tf_pkg_name in ['tensorflow', 'tensorflow-gpu', 'tf-nightly', 'tf-nightly-gpu']:
-    try:
-        tf_pkg = pkg_resources.get_distribution(tf_pkg_name)
-    except pkg_resources.DistributionNotFound:
-        pass
-assert tf_pkg is not None, 'TensorFlow needed, of version above 1.4'
-from distutils.version import LooseVersion
-assert LooseVersion(re.sub(r'-?rc\d+$', '', tf_pkg.version)) >= LooseVersion('1.4.0')