Add build matrix for Go and PG

.github/workflows/ci.yml

@@ -12,12 +12,17 @@ jobs:
     name: Test
     runs-on: ubuntu-latest
 
+    strategy:
+      matrix:
+        go_version: [1.14, 1.15]
+        pg_version: [9.6, 10, 11, 12, 13]
+
     steps:
 
     - name: Set up Go 1.x
       uses: actions/setup-go@v2
       with:
-        go-version: ^1.13
+        go-version: ${{ matrix.go_version }}
 
     - name: Check out code into the Go module directory
       uses: actions/checkout@v2
@@ -25,7 +30,7 @@ jobs:
     - name: Setup database server for testing
       run: ci/setup_test.bash
       env:
-        PGVERSION: 12
+        PGVERSION: ${{ matrix.pg_version }}
 
     - name: Test
       run: go test -v ./...