icu: update icudata generator URL

It was pointing to version 51.x which wouldn't work well with 55.x.

Point it to the latest version that matches the current buildroot
version (55). When a new ICU major version is released a link for the
"old" 55 version will be available below as is it currently for
previous versions such as 54, 53 and so on.

Signed-off-by: Gustavo Zacarias <gustavo.zacarias@free-electrons.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

package/icu/Config.in

@@ -19,9 +19,10 @@ config BR2_PACKAGE_ICU_CUSTOM_DATA_PATH
 	string "Path to custom data library file"
 	help
 	  This option allows to define the path to a custom data
-	  library generated with
-	  http://apps.icu-project.org/datacustom/ICUData51.html. Leave
-	  empty to not use this functionality.
+	  library generated with http://apps.icu-project.org/datacustom/
+	  Make sure you select the appropiate version to match the one
+	  provided by buildroot.
+	  Leave empty to not use this functionality.
 
 endif