Fix Swift sample build (#1202)

Author: paulb777

samples/swift/FirebaseUI-demo-swift.xcodeproj/project.pbxproj

@@ -774,7 +774,7 @@
 					"\"$(PODS_ROOT)/FirebaseUI/FirebaseDatabaseUI\"",
 				);
 				INFOPLIST_FILE = "FirebaseUI-demo-swift/Info.plist";
-				IPHONEOS_DEPLOYMENT_TARGET = 12.0;
+				IPHONEOS_DEPLOYMENT_TARGET = 15.0;
 				LD_RUNPATH_SEARCH_PATHS = "$(inherited) @executable_path/Frameworks";
 				PRODUCT_BUNDLE_IDENTIFIER = "com.google.firebase.firebaseui.FirebaseUI-demo-swift";
 				PRODUCT_NAME = "$(TARGET_NAME)";
@@ -813,7 +813,7 @@
 					"\"$(PODS_ROOT)/FirebaseUI/FirebaseDatabaseUI\"",
 				);
 				INFOPLIST_FILE = "FirebaseUI-demo-swift/Info.plist";
-				IPHONEOS_DEPLOYMENT_TARGET = 12.0;
+				IPHONEOS_DEPLOYMENT_TARGET = 15.0;
 				LD_RUNPATH_SEARCH_PATHS = "$(inherited) @executable_path/Frameworks";
 				PRODUCT_BUNDLE_IDENTIFIER = "com.google.firebase.firebaseui.FirebaseUI-demo-swift";
 				PRODUCT_NAME = "$(TARGET_NAME)";

samples/swift/FirebaseUI-demo-swift/Samples/Auth/FUICustomAuthUIDelegate.swift

@@ -15,6 +15,7 @@
 //
 
 import UIKit
+import FirebaseAuth
 import FirebaseEmailAuthUI
 
 class FUICustomAuthDelegate: NSObject, FUIAuthDelegate {

samples/swift/FirebaseUI-demo-swift/Samples/Auth/FUICustomPasswordVerificationViewController.swift

@@ -15,6 +15,7 @@
 //
 
 import UIKit
+import FirebaseAuth
 import FirebaseEmailAuthUI
 
 class FUICustomPasswordVerificationViewController: FUIPasswordVerificationViewController, UITextFieldDelegate {