Corrected types of page_info return value in documentation.

Summary:
I was confused by the current documentation, as it was requesting me to pass the previously received `end_cursor` into the next fetch but it was declared as a boolean. I checked in the debugger and it's just mislabeled in the docs, so this PR fixes the docs.

I tried to push this change back in #15472 but wasn't able to undo the borked rebase, so I'm submitting a new PR.

This is a change to documentation only.

[DOCS] [BUGFIX] [Libraries/CameralRoll/CameraRoll.js] - Corrected return type in the documentation for the `start_cursor` and `end_cursor` values.
Closes #16830

Differential Revision: D6371585

Pulled By: hramos

fbshipit-source-id: 5038041e95a04ea4c2de8d2b535a8a4e019289f6

Libraries/CameraRoll/CameraRoll.js

@@ -215,8 +215,8 @@ class CameraRoll {
    *              - `speed`: {number}
    * - `page_info` : {object} : An object with the following shape:
    *      - `has_next_page`: {boolean}
-   *      - `start_cursor`: {boolean}
-   *      - `end_cursor`: {boolean}
+   *      - `start_cursor`: {string}
+   *      - `end_cursor`: {string}
    *
    * Loading images:
    * ```