Add Python 3.9 wheels

Author: mattsplats

.travis.yml

@@ -41,6 +41,11 @@ matrix:
         - MB_PYTHON_VERSION=3.8
         - NP_BUILD_DEP="1.14.5"
         - NP_TEST_DEP="1.14.5"
+    - os: linux
+      env:
+        - MB_PYTHON_VERSION=3.9
+        - NP_BUILD_DEP="1.19.3"
+        - NP_TEST_DEP="1.93.3"
 
     - os: linux
       env:
@@ -82,6 +87,15 @@ matrix:
         - MB_ML_VER=2014
         - PLAT=aarch64
         - DOCKER_TEST_IMAGE=multibuild/xenial_arm64v8
+    - os: linux
+      arch: arm64-graviton2
+      env:
+        - MB_PYTHON_VERSION=3.9
+        - NP_BUILD_DEP="1.19.3"
+        - NP_TEST_DEP="1.19.3"
+        - MB_ML_VER=2014
+        - PLAT=aarch64
+        - DOCKER_TEST_IMAGE=multibuild/xenial_arm64v8
 
     - os: osx
       language: generic
@@ -104,6 +118,13 @@ matrix:
         - MB_PYTHON_OSX_VER=10.9
         - NP_BUILD_DEP=1.14.5
         - NP_TEST_DEP=1.14.5
+    - os: osx
+      language: generic
+      env:
+        - MB_PYTHON_VERSION=3.9
+        - MB_PYTHON_OSX_VER=10.9
+        - NP_BUILD_DEP=1.19.3
+        - NP_TEST_DEP=1.19.3
 before_install:
     # See:
     # https://github.com/travis-ci/travis-ci/issues/8920#issuecomment-352661024