[CLEANUP] update prettier to v2.0.4

tests/core/event_bus.test.ts

@@ -14,7 +14,7 @@ describe("event bus behaviour", () => {
     expect.assertions(1);
     const bus = new EventBus();
     const owner = {};
-    bus.on("event", owner, function(this: any) {
+    bus.on("event", owner, function (this: any) {
       expect(this).toBe(owner);
     });
     bus.trigger("event");

tests/core/observer.test.ts

@@ -22,7 +22,7 @@ describe("observer", () => {
     expect(observer.rev).toBe(2);
 
     expect(obj2).toEqual({
-      a: 2
+      a: 2,
     });
   });
 
@@ -47,7 +47,7 @@ describe("observer", () => {
     expect(observer.rev).toBe(5);
     expect(obj).toEqual({
       a: null,
-      b: undefined
+      b: undefined,
     });
   });