support python 3.8 (#351)

* support python 3.8

* fix python2 compatibility

* remove py38 unittest since paddle don't support python3.8

.teamcity/CHANGELOG.md

 ### [2019-07-09] 1.1-cuda9.0-cudnn7-docs:
 add unnit test for compling the docs
   - add an envionment `docs` in anaconda 
+
+### [2020-07-16] cuda9.0-cudnn7-v3:
+add python3.8 env

.teamcity/Dockerfile

@@ -15,7 +15,7 @@
 
 # A dev image based on paddle production image
 
-FROM parl/parl-test:cuda9.0-cudnn7-v2
+FROM parl/parl-test:cuda9.0-cudnn7-v3
 
 COPY ./requirements.txt /root/
 

setup.py

@@ -72,7 +72,8 @@ setup(
     install_requires=[
         "termcolor>=1.1.0",
         "pyzmq==18.0.1",
-        "pyarrow==0.13.0",
+        'pyarrow==0.16.0; python_version<"3"',
+        'pyarrow==0.17.1; python_version>="3"',
         "scipy>=1.0.0",
         "cloudpickle==1.2.1",
         "tensorboardX==1.8",