Update config.yml

Update CI to use Python 3.7 / 3.8 as 3.6 is no longer supported

.circleci/config.yml

@@ -2,9 +2,9 @@ version: 2
 
 jobs:
 
-  build-python36:
+  build-python37:
     docker:
-      - image: python:3.6
+      - image: python:3.7
     steps:
       - checkout
       - restore_cache:
@@ -19,9 +19,9 @@ jobs:
       - run: git submodule update --init
       - run: make test
 
-  build-python37:
+  build-python38:
     docker:
-      - image: python:3.7
+      - image: python:3.8
     steps:
       - checkout
       - restore_cache:
@@ -40,6 +40,6 @@ workflows:
   version: 2
   build:
     jobs:
-      - build-python36
       - build-python37
-      #- build-python38 # no tensorflow for python 3.8
+      - build-python38
+