execabs: isGo119ErrDot: use errors.Is instead of string-matching

Addresses the TODO added in CL 403256.

Change-Id: Iae44242e00b6a309cc0f1e336462bc2d4995a5e2
GitHub-Last-Rev: 1adfdb7
GitHub-Pull-Request: #142
Reviewed-on: https://go-review.googlesource.com/c/sys/+/448877
Auto-Submit: Ian Lance Taylor <iant@google.com>
Run-TryBot: Ian Lance Taylor <iant@google.com>
Reviewed-by: Michael Knyszek <mknyszek@google.com>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@google.com>

execabs/execabs_go119.go

@@ -7,9 +7,11 @@
 
 package execabs
 
-import "strings"
+import (
+	"errors"
+	"os/exec"
+)
 
 func isGo119ErrDot(err error) bool {
-	// TODO: return errors.Is(err, exec.ErrDot)
-	return strings.Contains(err.Error(), "current directory")
+	return errors.Is(err, exec.ErrDot)
 }