Enable Windows build.

.github/workflows/build.yml

diff --git a/.github/workflows/build.yml b/.github/workflows/build.yml
index 3b0d9ff..06d92cf 100644
--- a/.github/workflows/build.yml
+++ b/.github/workflows/build.yml
@@ -6,8 +6,8 @@
     runs-on: ${{ matrix.os }}
     strategy:
       matrix:
-#        os: [macos-latest, ubuntu-latest, windows-latest]
-        os: [macos-latest, ubuntu-latest]
+        os: [macos-latest, ubuntu-latest, windows-latest]
+#        os: [macos-latest, ubuntu-latest]
     steps:
       - name: checkout
         uses: actions/checkout@v2