Use Prettier JS (#5017)

* Adds prettier

* Run lint before tests

spec/PromiseRouter.spec.js

@@ -1,25 +1,33 @@
-const PromiseRouter = require("../lib/PromiseRouter").default;
+const PromiseRouter = require('../lib/PromiseRouter').default;
 
-describe("PromiseRouter", () => {
-  it("should properly handle rejects", (done) => {
+describe('PromiseRouter', () => {
+  it('should properly handle rejects', done => {
     const router = new PromiseRouter();
-    router.route("GET", "/dummy", ()=> {
-      return Promise.reject({
-        error: "an error",
-        code: -1
-      })
-    }, () => {
-      fail("this should not be called");
-    });
+    router.route(
+      'GET',
+      '/dummy',
+      () => {
+        return Promise.reject({
+          error: 'an error',
+          code: -1,
+        });
+      },
+      () => {
+        fail('this should not be called');
+      }
+    );
 
-    router.routes[0].handler({}).then((result) => {
-      jfail(result);
-      fail("this should not be called");
-      done();
-    }, (error)=> {
-      expect(error.error).toEqual("an error");
-      expect(error.code).toEqual(-1);
-      done();
-    });
+    router.routes[0].handler({}).then(
+      result => {
+        jfail(result);
+        fail('this should not be called');
+        done();
+      },
+      error => {
+        expect(error.error).toEqual('an error');
+        expect(error.code).toEqual(-1);
+        done();
+      }
+    );
   });
-})
+});