Update description about .number modifier (#1285)

* Update description about .number modifier

* Update src/guide/forms.md

Co-authored-by: Natalia Tepluhina <tarya.se@gmail.com>

Author: zxuqian

Diff for: src/guide/forms.md

@@ -269,10 +269,10 @@ By default, `v-model` syncs the input with the data after each `input` event (wi
 If you want user input to be automatically typecast as a number, you can add the `number` modifier to your `v-model` managed inputs:
 
 ```html
-<input v-model.number="age" type="number" />
+<input v-model.number="age" type="text" />
 ```
 
-This is often useful, because even with `type="number"`, the value of HTML input elements always returns a string. If the value cannot be parsed with `parseFloat()`, then the original value is returned.
+This is often useful when the input type is `text`. If the input type is `number`, Vue can automatically convert the raw string value to a number, and you don't need to add the `.number` modifier to `v-model`. If the value cannot be parsed with `parseFloat()`, then the original value is returned.
 
 ### `.trim`