make the callbacks optional on firebase simple login

firebase/firebase-simplelogin-tests.ts

@@ -59,20 +59,28 @@ auth.createUser(email, password, function(error, user) {
     }
 });
 
+auth.createUser(email, password);
+
 auth.changePassword(email, oldPassword, newPassword, function(error, success) {
     if (!error) {
         console.log('Password changed successfully');
     }
 });
 
+auth.changePassword(email, oldPassword, newPassword);
+
 auth.sendPasswordResetEmail(email, function(error, success) {
     if (!error) {
         console.log('Password reset email sent successfully');
     }
 });
 
+auth.sendPasswordResetEmail(email);
+
 auth.removeUser(email, password, function(error, success) {
     if (!error) {
         console.log('User deleted successfully');
     }
-});
+});
+
+auth.removeUser(email, password);

firebase/firebase-simplelogin.d.ts

@@ -86,9 +86,9 @@ declare class FirebaseSimpleLogin {
                    callback?: (err: IFirebaseSimpleLoginError, success: boolean) => any): void;
 
     sendPasswordResetEmail(email: string,
-                           callback: (err: IFirebaseSimpleLoginError, success: boolean) => any): void;
+                           callback?: (err: IFirebaseSimpleLoginError, success: boolean) => any): void;
 
     removeUser(email: string,
                password: string,
-               callback: (err: IFirebaseSimpleLoginError, success: boolean) => any): void;
+               callback?: (err: IFirebaseSimpleLoginError, success: boolean) => any): void;
 }