Drop python 3.7 test in favor of 3.10

This does NOT mean Python 3.7 is no longer supported. Just trying to keep
the number of builds a little reasonable.

Author: mwcraig

.github/workflows/build.yml

@@ -9,7 +9,7 @@ jobs:
       max-parallel: 4
       fail-fast: false
       matrix:
-        python-version: [3.7, 3.8, 3.9]
+        python-version: [3.8, 3.9, 3.10]
         platform: [ubuntu-latest, macos-latest, windows-latest]
     runs-on: ${{ matrix.platform }}