One step for 1.12, one step for 1.13

.github/workflows/go.yml

@@ -1,24 +1,34 @@
 name: Go
 on: [push]
 jobs:
-
-  build:
-    name: Build
+  build-1.12:
+    name: Build with Go 1.12
     runs-on: ubuntu-latest
     steps:
+    - name: Set up Go 1.12
+      uses: actions/setup-go@v1
+      with:
+        go-version: 1.12
+      id: go
+    - name: Check out code into the Go module directory
+      uses: actions/checkout@v1
+    - name: Test
+      run: go test -mod vendor ./...
+    - name: Build
+      run: go build -mod vendor
 
+  build-1.13:
+    name: Build with Go 1.13
+    runs-on: ubuntu-latest
+    steps:
       - name: Set up Go 1.13
         uses: actions/setup-go@v1
         with:
           go-version: 1.13
         id: go
-
       - name: Check out code into the Go module directory
         uses: actions/checkout@v1
-      
       - name: Test
         run: go test -mod vendor ./...
-
-
       - name: Build
         run: go build -mod vendor