Update minimum go version to 1.13

.github/workflows/pr.yml

@@ -13,10 +13,10 @@ jobs:
         os: [ubuntu-latest, windows-latest, macOS-latest]
     steps:
 
-    - name: Set up Go 1.12
+    - name: Set up Go 1.13
       uses: actions/setup-go@v1
       with:
-        go-version: 1.12
+        go-version: 1.13
       id: go
 
     - name: Check out code into the Go module directory
@@ -27,6 +27,6 @@ jobs:
         go get -v -d ./...
     - name: Build
       run: go build -v ./cmd/wails
-    
+
     - name: Test
       run: ./wails version