golangci-lint: enable mirror linter

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

.golangci.yml

@@ -41,6 +41,7 @@ linters:
     - govet
     - importas                  # Enforces consistent import aliases.
     - ineffassign
+    - mirror                    # Detects wrong mirror patterns of bytes/strings usage.
     - misspell                  # Detects commonly misspelled English words in comments.
     - nakedret                  # Detects uses of naked returns.
     - nilerr                    # Detects code that returns nil even if it checks that the error is not nil.

cli/command/swarm/ca_test.go

@@ -69,7 +69,7 @@ func writeFile(data string) (string, error) {
 	if err != nil {
 		return "", err
 	}
-	_, err = tmpfile.Write([]byte(data))
+	_, err = tmpfile.WriteString(data)
 	if err != nil {
 		return "", err
 	}

e2e/cli-plugins/socket_test.go

@@ -58,7 +58,7 @@ func TestPluginSocketBackwardsCompatible(t *testing.T) {
 
 			ptmx, err := pty.Start(command)
 			assert.NilError(t, err, "failed to launch command with fake TTY")
-			_, _ = ptmx.Write([]byte("hello!"))
+			_, _ = ptmx.WriteString("hello!")
 
 			done := make(chan error)
 			go func() {