Test and lint against Go 1.19 (#62)

Add Go 1.19 to the test matrix, and switch linting to Go 1.19 since we
prefer to lint with the latest stable release.
With Go 1.19, we need to:

Update tools dependencies
Fix any use of ioutil
gofmt all files to match new godoc format

.github/workflows/go.yml

@@ -13,9 +13,9 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        go: ["1.17.x", "1.18.x"]
+        go: ["1.17.x", "1.18.x", "1.19.x"]
         include:
-        - go: 1.18.x
+        - go: 1.19.x
           latest: true
 
     steps:

appendinvoke_example_test.go

@@ -22,7 +22,6 @@ package multierr_test
 
 import (
 	"fmt"
-	"io/ioutil"
 	"log"
 	"os"
 	"path/filepath"
@@ -37,7 +36,7 @@ func ExampleAppendInvoke() {
 }
 
 func run() (err error) {
-	dir, err := ioutil.TempDir("", "multierr")
+	dir, err := os.MkdirTemp("", "multierr")
 	// We create a temporary directory and defer its deletion when this
 	// function returns.
 	//