Fix compile

app/src/main/java/org/tasks/preferences/Preferences.java

@@ -2,6 +2,7 @@ package org.tasks.preferences;
 
 import static android.content.SharedPreferences.Editor;
 import static com.google.common.collect.Iterables.transform;
+import static com.google.common.collect.Sets.newHashSet;
 import static com.todoroo.andlib.utility.AndroidUtilities.atLeastKitKat;
 import static java.util.Collections.emptySet;