Update Gutenberg ref

Author: Gerardo

build.gradle

@@ -23,7 +23,7 @@ ext {
     automatticAboutVersion = '1.4.0'
     automatticRestVersion = '1.0.8'
     automatticTracksVersion = '5.0.0'
-    gutenbergMobileVersion = '6878-64fe89bbf66583e5a7f93fd2d28de3342f14ce85'
+    gutenbergMobileVersion = 'v1.120.0-alpha1'
     wordPressAztecVersion = 'v2.1.3'
     wordPressFluxCVersion = 'trunk-a9a471914d3ebd1093986d3d0a95c2a29b29dca0'
     wordPressLoginVersion = '1.15.0'