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

This 'FluxC' hash updates the library to that 'trunk' version
where the 'Media' model classes are updated to their new null proof
version.

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

build.gradle

@@ -22,7 +22,7 @@ ext {
     automatticTracksVersion = '3.3.0'
     gutenbergMobileVersion = 'v1.107.0'
     wordPressAztecVersion = 'v1.8.0'
-    wordPressFluxCVersion = 'trunk-8712ec791066f2d86bb9aa6d21710ee7075fac05'
+    wordPressFluxCVersion = 'trunk-e71a4dc765b7785f753e9224512e0a76c43104e4'
     wordPressLoginVersion = 'trunk-9963d78096edf65f8704b803e5b93c08fc9174cd'
     wordPressPersistentEditTextVersion = '1.0.2'
     wordPressUtilsVersion = '3.10.0'