Add Py3.9 to travis build matrix.

Author: scoder

.travis.yml

@@ -20,6 +20,10 @@ matrix:
     language: generic
     env:
     - MB_PYTHON_VERSION=2.7
+  - os: osx
+    language: generic
+    env:
+    - MB_PYTHON_VERSION=3.9
   - os: osx
     language: generic
     env:
@@ -107,6 +111,20 @@ matrix:
     - PLAT=aarch64
     - MB_ML_VER=2014
     - DOCKER_TEST_IMAGE=multibuild/xenial_arm64v8
+  - os: linux
+    env:
+    - MB_PYTHON_VERSION=3.9
+  - os: linux
+    env:
+    - MB_PYTHON_VERSION=3.9
+    - PLAT=i686
+  - os: linux
+    arch: arm64
+    env:
+    - MB_PYTHON_VERSION=3.9
+    - PLAT=aarch64
+    - MB_ML_VER=2014
+    - DOCKER_TEST_IMAGE=multibuild/xenial_arm64v8
 
 before_install:
 - source multibuild/common_utils.sh