support --output-directory when running in Docker

cli/Dockerfile

@@ -7,6 +7,6 @@ WORKDIR /usr/src/app/node_modules/single-file/cli
 ENTRYPOINT [ \
     "./single-file", \
     "--browser-executable-path", "/usr/bin/chromium-browser", \
-    "--output-directory", "./../../../out", \
+    "--output-directory", "./../../../out/", \
     "--browser-args", "[\"--no-sandbox\"]", \
     "--dump-content" ]

cli/single-file-cli-api.js

@@ -272,6 +272,9 @@ async function capturePage(options) {
 }
 
 function getFilename(filename, options, index = 1) {
+	if (Array.isArray(options.outputDirectory)) {
+		options.outputDirectory = options.outputDirectory.join("");
+	}
 	let outputDirectory = options.outputDirectory || "";
 	if (outputDirectory && !outputDirectory.endsWith("/")) {
 		outputDirectory += "/";