Update ngsi_ckan_sink.md

This URL has changed to https://symbl.cc/

doc/cygnus-ngsi-ld/flume_extensions_catalogue/ngsi_ckan_sink.md

@@ -375,7 +375,7 @@ From version 1.3.0 (included), Cygnus applies this specific encoding tailored to
 * Underscore character, `_`, is not encoded.
 * Hyphen character, `-`, is not encoded.
 * Equals character, `=`, is encoded as `xffff`.
-* All other characters, including the slash in the FIWARE service paths, are encoded as a `x` character followed by the [Unicode](http://unicode-table.com) of the character.
+* All other characters, including the slash in the FIWARE service paths, are encoded as a `x` character followed by the [Unicode](https://symbl.cc) of the character.
 * User defined strings composed of a `x` character and a Unicode are encoded as `xx` followed by the Unicode.
 * `xffff` is used as concatenator character.