update workflow build environment to py37 (#1172)

Author: rainyfly

.github/workflows/build.yml

@@ -7,7 +7,7 @@ jobs:
     strategy:
       matrix:
         os: [ubuntu-latest, macos-latest]
-        python-version: ['3.5']
+        python-version: ['3.7']
         node-version: ['14']
     steps:
       - name: Checkout