updating tests to 3.9

.github/workflows/build.yml

@@ -1,4 +1,4 @@
-name: Build and Test [Python 3.7, 3.8, 3.9]
+name: Build and Test [Python 3.9]
 
 on: push
 
@@ -7,7 +7,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        python-version: [3.7, 3.8, 3.9]
+        python-version: [3.9]
 
     steps:
       - uses: actions/checkout@v2