fix: add hijri (islamic) to CalendarSystem type export

Author: amirhmoradi

Diff for: types/index.d.ts

@@ -5,7 +5,7 @@ import { CalendarSystemBase } from './calendarSystems/CalendarSystemBase';
 // All Calendar Systems known to Intl API (alphabetical order)
 // 'buddhist' | 'chinese' | 'coptic' | 'dangi' | 'ethioaa' | 'ethiopic' | 'gregory' | 'hebrew' | 'indian' | 'islamic' | 'islamic-civil' | 'islamic-rgsa' | 'islamic-tbla' | 'islamic-umalqura' | 'islamicc' | 'iso8601' | 'japanese' | 'persian' | 'roc'
 // Our supported Calendar Systems (alphabetical order)
-export type CalendarSystem = 'gregory' | 'persian';
+export type CalendarSystem = 'gregory' | 'persian' | 'islamic';
 // TODO: export type CalendarSystem = 'gregory' | 'persian' | 'islamic' | 'islamic-umalqura' | 'hebrew' | 'ethiopic';
 // ! Note that we use the default "islamic-umalqura" calendar system for "islamic" calendar system