run ci on linux and macos

Author: mirca

.github/workflows/pythonpackage.yml

@@ -1,15 +1,16 @@
-name: Python package
+name: riskparity-tests
 
 on: [push]
 
 jobs:
   build:
 
-    runs-on: ubuntu-latest
+    runs-on: ${{ matrix.os }}
     strategy:
-      max-parallel: 4
+      max-parallel: 9
       matrix:
-        python-version: [3.7, 3.8]
+        python-version: [3.7, 3.8, 3.9]
+        os: [macos-latest, ubuntu-latest]
 
     steps:
     - uses: actions/checkout@v1