Treat UGX as a decimal based currency. (#1320)

Stripe documents several currencies as Zero-decimal currencies, these currencies should be charged as “$1 = 1” in the stripe API.

https://docs.stripe.com/currencies#zero-decimal

However, for backwards compatibility, specific zero-decimal currencies must be treated as decimal currencies, this includes UGX and ISK (which is not documented as a zero-decimal in the above documentation)

This means that when we've attempted to charge `1,000 UGX` we've actually charged `10.00 UGX = 10 UGX`.

public_html/wp-content/mu-plugins/utilities/class-stripe-client.php

@@ -191,7 +191,7 @@ public static function get_fractional_unit_amount( $order_currency, $base_unit_a
 		$currency_multipliers = array(
 			// Zero-decimal currencies.
 			1   => array(
-				'BIF', 'CLP', 'DJF', 'GNF', 'JPY', 'KMF', 'KRW', 'MGA', 'PYG', 'RWF', 'UGX', 'VND', 'VUV', 'XAF',
+				'BIF', 'CLP', 'DJF', 'GNF', 'JPY', 'KMF', 'KRW', 'MGA', 'PYG', 'RWF', 'VND', 'VUV', 'XAF',
 				'XOF', 'XPF',
 			),
 			100 => array(
@@ -204,7 +204,7 @@ public static function get_fractional_unit_amount( $order_currency, $base_unit_a
 				'MXN', 'MYR', 'MZN', 'NAD', 'NGN', 'NIO', 'NOK', 'NPR', 'NZD', 'PAB', 'PEN', 'PGK', 'PHP', 'PKR',
 				'PLN', 'QAR', 'RON', 'RSD', 'RUB', 'SAR', 'SBD', 'SCR', 'SEK', 'SGD', 'SHP', 'SLL',
 				'SOS', 'SRD', 'STD', 'SZL', 'THB', 'TJS', 'TOP', 'TRY', 'TTD', 'TWD',
-				'TZS', 'UAH', 'USD', 'UYU', 'UZS', 'WST', 'XCD', 'YER', 'ZAR', 'ZMW',
+				'TZS', 'UAH', 'UGX', 'USD', 'UYU', 'UZS', 'WST', 'XCD', 'YER', 'ZAR', 'ZMW',
 			),
 		);