Hubble gallery: enable AUM and correct category

metadata/com.derek_s.hubble_gallery.txt

@@ -1,4 +1,4 @@
-Categories:System
+Categories:Multimedia
 License:Apache2
 Web Site:
 Source Code:https://github.com/derekcsm/hubble_gallery
@@ -22,5 +22,5 @@ Build:1.5.0,20
         sed -i -e '/crashlytics/,+2d' -e '/fabric/d' build.gradle && \
         sed -i -e '/Crashlytics/d' -e '/fabric/d' src/release/java/com/derek_s/hubble_gallery/base/HubbleApplicationRelease.java
 
-Auto Update Mode:None
+Auto Update Mode:Version %v
 Update Check Mode:Tags