handle absolute path

cli/single-file-cli-api.js

@@ -273,7 +273,12 @@ async function capturePage(options) {
 
 function getFilename(filename, options, index = 1) {
 	if (Array.isArray(options.outputDirectory)) {
-		options.outputDirectory = options.outputDirectory.join("");
+		const outputDirectory = options.outputDirectory.pop();
+		if (outputDirectory.startsWith("/")) {
+			options.outputDirectory = outputDirectory;
+		} else {
+			options.outputDirectory = options.outputDirectory.join("");
+		}
 	}
 	let outputDirectory = options.outputDirectory || "";
 	if (outputDirectory && !outputDirectory.endsWith("/")) {