Add new balance transaction methods (#1423)

* Add new balance transaction methods

* wip

* Update ManagesCustomer.php

Co-authored-by: Taylor Otwell <taylorotwell@gmail.com>

src/Concerns/ManagesCustomer.php

@@ -317,6 +317,32 @@ public function balanceTransactions($limit = 10, array $options = [])
         });
     }
 
+    /**
+     * Credit a customer's balance.
+     *
+     * @param  int  $amount
+     * @param  string|null  $description
+     * @param  array  $options
+     * @return \Laravel\Cashier\CustomerBalanceTransaction
+     */
+    public function creditBalance($amount, $description = null, array $options = [])
+    {
+        return $this->applyBalance(-$amount, $description, $options);
+    }
+
+    /**
+     * Debit a customer's balance.
+     *
+     * @param  int  $amount
+     * @param  string|null  $description
+     * @param  array  $options
+     * @return \Laravel\Cashier\CustomerBalanceTransaction
+     */
+    public function debitBalance($amount, $description = null, array $options = [])
+    {
+        return $this->applyBalance($amount, $description, $options);
+    }
+
     /**
      * Apply a new amount to the customer's balance.
      *