minor symfony#17617 [Form] fix option name in upgrade file (xabbuh)

This PR was merged into the 2.8 branch.

Discussion
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[Form] fix option name in upgrade file

| Q             | A
| ------------- | ---
| Fixed tickets |
| License       | MIT

Commits
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0efb137 [Form] fix option name in upgrade file

Author: fabpot

UPGRADE-2.8.md

@@ -22,7 +22,7 @@ Form
    of the new `csrf_token_id` option.
 
  * The `csrf_provider` option was deprecated and will be removed in 3.0 in favor
-   of the new `csrf_token_generator` option.
+   of the new `csrf_token_manager` option.
 
  * The "cascade_validation" option was deprecated. Use the "constraints"
    option together with the `Valid` constraint instead. Contrary to