fix typo

Author: stefanseifert

src/site/markdown/extensions.md

@@ -88,7 +88,7 @@ Example for additionally adding binary files to the content package:
       rootPath: /content/files
       files:
       # Add a static file from the class paths (or other URLs)
-      - url:classpath:/my-resources/file1.txt
+      - url: classpath:/my-resources/file1.txt
         path: /content/files/file1.txt
       # Add a file that was generated by CONGA (delete after inclusion in package)
       - file: generated-file.txt