Added 'setDefault' to Moment Timezone definition

moment-timezone/moment-timezone-tests.ts

@@ -75,3 +75,5 @@ moment.tz.load({
 });
 
 moment.tz.names();
+
+moment.tz.setDefault('America/Los_Angeles');

moment-timezone/moment-timezone.d.ts

@@ -68,6 +68,8 @@ interface MomentTimezone {
     }): void;
 
     names(): string[];
+
+    setDefault(timezone: string): void;
 }
 
 declare module 'moment-timezone' {