switched to default export in TS typing (#468)

src/types/evented.d.ts

@@ -11,4 +11,4 @@ declare class Evented {
     trigger(event: string): void;
 }
 
-export = Evented;
+export default Evented;

src/types/shepherd.d.ts

@@ -8,4 +8,4 @@ declare abstract class Shepherd extends Evented {
     static Evented: { new(): Evented };
 }
 
-export = Shepherd;
+export default Shepherd;

src/types/step.d.ts

@@ -226,4 +226,4 @@ declare class Step extends Evented {
     show(): Promise<void> | void;
 }
 
-export = Step;
+export default Step;

src/types/tour.d.ts

@@ -127,4 +127,4 @@ declare class Tour extends Evented {
     start(): void;
 }
 
-export = Tour;
+export default Tour;