Make all builders final

Signed-off-by: Alex Saveau <saveau.alexandre@gmail.com>

Author: SUPERCILEX

common/src/main/java/com/firebase/ui/common/Preconditions.java

@@ -6,7 +6,7 @@
  * Convenience class for checking argument conditions.
  */
 @RestrictTo(RestrictTo.Scope.LIBRARY_GROUP)
-public class Preconditions {
+public final class Preconditions {
 
     public static <T> T checkNotNull(T o) {
         if (o == null) throw new IllegalArgumentException("Argument cannot be null.");

database/src/main/java/com/firebase/ui/database/FirebaseListOptions.java

@@ -16,7 +16,7 @@
  *
  * @see Builder
  */
-public class FirebaseListOptions<T> {
+public final class FirebaseListOptions<T> {
 
     private static final String ERR_SNAPSHOTS_SET = "Snapshot array already set. " +
             "Call only one of setSnapshotArray, setQuery, or setIndexedQuery.";
@@ -62,7 +62,7 @@ public LifecycleOwner getOwner() {
      *
      * @param <T> the model class for the {@link FirebaseListAdapter}.
      */
-    public static class Builder<T> {
+    public static final class Builder<T> {
 
         private ObservableSnapshotArray<T> mSnapshots;
         private @LayoutRes Integer mLayout;

database/src/main/java/com/firebase/ui/database/FirebaseRecyclerOptions.java

@@ -15,7 +15,7 @@
  *
  * @see Builder
  */
-public class FirebaseRecyclerOptions<T> {
+public final class FirebaseRecyclerOptions<T> {
 
     private static final String ERR_SNAPSHOTS_SET = "Snapshot array already set. " +
             "Call only one of setSnapshotArray, setQuery, or setIndexedQuery.";
@@ -53,7 +53,7 @@ public LifecycleOwner getOwner() {
      *
      * @param <T> the model class for the {@link FirebaseRecyclerAdapter}.
      */
-    public static class Builder<T> {
+    public static final class Builder<T> {
 
         private ObservableSnapshotArray<T> mSnapshots;
         private LifecycleOwner mOwner;

firestore/src/main/java/com/firebase/ui/firestore/FirestoreRecyclerOptions.java

@@ -15,7 +15,7 @@
  *
  * @see Builder
  */
-public class FirestoreRecyclerOptions<T> {
+public final class FirestoreRecyclerOptions<T> {
 
     private static final String ERR_SNAPSHOTS_SET = "Snapshot array already set. " +
             "Call only one of setSnapshotArray or setQuery";
@@ -52,7 +52,7 @@ public LifecycleOwner getOwner() {
      *
      * @param <T> the model class for the {@link FirestoreRecyclerAdapter}.
      */
-    public static class Builder<T> {
+    public static final class Builder<T> {
 
         private ObservableSnapshotArray<T> mSnapshots;
         private LifecycleOwner mOwner;