Build: Update fluxc version to pr hash (#2886)

This 'FluxC' PR hash updates the library to that branch version
where the 'MediaModel' is updated to its new null proof version.

FluxC PR: https://github.com/wordpress-mobile/
WordPress-FluxC-Android/pull/2886

This step is required in order to check that these 'FluxC'
related changes work as expected for WPAndroid.

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FYI: This change is an addition to
f6f9375. This change is necessary in
order to overcome and resolve new merge conflicts.

build.gradle

@@ -22,7 +22,7 @@ ext {
     automatticTracksVersion = '3.3.0'
     gutenbergMobileVersion = 'v1.107.0'
     wordPressAztecVersion = 'v1.8.0'
-    wordPressFluxCVersion = 'trunk-82a701e28d0eeb8c1612b256fd9d772182a13b6a'
+    wordPressFluxCVersion = '2886-feea7f92db822907a344d2f04195da23155a88bd'
     wordPressLoginVersion = 'trunk-9963d78096edf65f8704b803e5b93c08fc9174cd'
     wordPressPersistentEditTextVersion = '1.0.2'
     wordPressUtilsVersion = '3.10.0'