erp5_web_renderjs_ui&test: first line of Appcache file should be CACHE MANIFEST

https://developer.mozilla.org/en-US/docs/Web/HTML/Using_the_application_cache:

The first line of the cache manifest must consist of the string CACHE MANIFEST (with a single U+0020 space between the two words), 

followed by zero or more space or tab characters. Any other text on the line is ignored.