format promise.mdx

Author: theqp

pages/docs/manual/latest/promise.mdx

@@ -41,19 +41,16 @@ Using the [pipe operator](pipe.md):
 ```res example
 let myPromise = Js.Promise.make((~resolve, ~reject) => resolve(. 2))
 
-myPromise
--> Js.Promise.then_(value => {
-     Js.log(value)
-     Js.Promise.resolve(value + 2)
-   }, _)
--> Js.Promise.then_(value => {
-     Js.log(value)
-     Js.Promise.resolve(value + 3)
-   }, _)
--> Js.Promise.catch(err => {
-     Js.log2("Failure!!", err)
-     Js.Promise.resolve(-2)
-   }, _)
+myPromise->Js.Promise.then_(value => {
+  Js.log(value)
+  Js.Promise.resolve(value + 2)
+}, _)->Js.Promise.then_(value => {
+  Js.log(value)
+  Js.Promise.resolve(value + 3)
+}, _)->Js.Promise.catch(err => {
+  Js.log2("Failure!!", err)
+  Js.Promise.resolve(-2)
+}, _)
 ```
 ```js
 var myPromise = new Promise(function (resolve, reject) {