fix: Don't double backslashes in shellQuote

internal/cmd/shellquote_test.go

@@ -14,8 +14,10 @@ func TestShellQuote(t *testing.T) {
 		`'`:           `\'`,
 		`''`:          `\'\'`,
 		`'a'`:         `\''a'\'`,
-		`\`:           `'\\'`,
-		`\a`:          `'\\a'`,
+		`\`:           `'\'`,
+		`\'`:          `'\'\'`,
+		`\a`:          `'\a'`,
+		`\n`:          `'\n'`,
 		`$a`:          `'$a'`,
 		`a`:           `a`,
 		`a/b`:         `a/b`,