Fixing error handling samples (#216)

Author: nadeesha

website/content/guide/binding.md

@@ -80,7 +80,7 @@ type User struct {
 ```go
 e.POST("/users", func(c echo.Context) (err error) {
   u := new(User)
-  if err = c.Bind(u); err != nil {
+  if err := c.Bind(u); err != nil {
     return
   }
   // To avoid security flaws try to avoid passing bound structs directly to other methods 
@@ -195,7 +195,7 @@ type CustomBinder struct {}
 func (cb *CustomBinder) Bind(i interface{}, c echo.Context) (err error) {
   // You may use default binder
   db := new(echo.DefaultBinder)
-  if err = db.Bind(i, c); err != echo.ErrUnsupportedMediaType {
+  if err := db.Bind(i, c); err != echo.ErrUnsupportedMediaType {
     return
   }