Fixed warnings

* BUG FIX: Removed warnings of missing 'code' for currency code when adding currency to Gravity Form options.

* ENHANCEMENT: Removed USD as this is redundant and exists by Gravity Forms default.

class-gf-paystack.php

@@ -1926,7 +1926,8 @@ public function add_paystack_currencies($currencies)
 				'symbol_padding'     => ' ',
 				'thousand_separator' => ',',
 				'decimal_separator'  => '.',
-				'decimals'           => 2
+				'decimals'           => 2,
+				'code'				 => 'NGN'
 			);
 		}
 
@@ -1940,7 +1941,8 @@ public function add_paystack_currencies($currencies)
 				'symbol_padding'     => ' ',
 				'thousand_separator' => ',',
 				'decimal_separator'  => '.',
-				'decimals'           => 2
+				'decimals'           => 2,
+				'code'				 => 'GHS'
 			);
 		}
 
@@ -1954,24 +1956,12 @@ public function add_paystack_currencies($currencies)
 				'symbol_padding'     => ' ',
 				'thousand_separator' => ',',
 				'decimal_separator'  => '.',
-				'decimals'           => 2
-			);
-		}
-
-		// Check if the currency is already registered.
-		if (!array_key_exists('USD', $currencies)) {
-			// Add USD to the list of supported currencies.
-			$currencies['USD'] = array(
-				'name'               => 'United States Dollar',
-				'symbol_left'        => '$',
-				'symbol_right'       => '',
-				'symbol_padding'     => ' ',
-				'thousand_separator' => ',',
-				'decimal_separator'  => '.',
-				'decimals'           => 2
+				'decimals'           => 2,
+				'code'				 => 'ZAR'
 			);
 		}
 
+
 		// Check if the currency is already registered.
 		if (!array_key_exists('KES', $currencies)) {
 			// Add KES to the list of supported currencies.
@@ -1982,7 +1972,8 @@ public function add_paystack_currencies($currencies)
 				'symbol_padding'     => ' ',
 				'thousand_separator' => ',',
 				'decimal_separator'  => '.',
-				'decimals'           => 2
+				'decimals'           => 2,
+				'code'				 => 'KES'
 			);
 		}