echo: Regression: binding a map is not allowed anymore

Issue Description

I think a valid use case of binding to a map[string]interface{} now causes the following error: Binding element must be a struct. I think the regression has been caused by #972.

Is this use case still valid ?

Checklist

• Dependencies installed
• No typos
• Searched existing issues and docs

Expected behaviour

Binding a map[string]interface{} is valid.

Actual behaviour

Binding a map[string]interface{} causes an error.

Code to debug

package main

func handler(c echo.Context) {
  var m map[string]interface{}
  if err := c.Bind(&m); err != nil {
    // err is "Binding element must be a struct"
  }
  return nil
}

Version/commit

1e9845a414f5177986779ee21963df7d1e362e15