JS: Also extract .njk files

Author: asgerf

javascript/extractor/src/com/semmle/js/extractor/FileExtractor.java

@@ -104,7 +104,7 @@ private static int skipBOM(byte[] bytes, int length) {
 
   /** Information about supported file types. */
   public static enum FileType {
-    HTML(".htm", ".html", ".xhtm", ".xhtml", ".vue", ".hbs", ".ejs") {
+    HTML(".htm", ".html", ".xhtm", ".xhtml", ".vue", ".hbs", ".ejs", ".njk") {
       @Override
       public IExtractor mkExtractor(ExtractorConfig config, ExtractorState state) {
         return new HTMLExtractor(config, state);