public function update(Request $request, $id)
{
    $this->validate($request, [
        'title' => 'required',
        'body' => 'required'
    ]);

    $post = Post::find($id); // We could use this here because it's declared on top (Post model)
    $post->title = $request->input('title');
    $post->body = $request->input('body');
    $post->user_id = auth()->user()->id;
    $post->save();

    return redirect('/posts')->with('success', 'Post Updated');
}

@extends('layouts.app')

@section('content')
    <h1>Create Post</h1>
    {!! Form::open(['action' => 'PostsController@store', 'method' => 'POST']) !!}
        <div class="form-group">
            {{Form::label('title', 'Title')}}
            {{Form::text('title', '', ['class' => 'form-control', 'placeholder' => 'Title'])}}
        </div>

    <div class="form-group">
        {{Form::label('body', 'Body')}}
        {{Form::textarea('body', '', ['id' => 'article-ckeditor', 'class' => 'form-control', 'placeholder' => 'Body Text'])}}
    </div>
    {{Form::submit('Submit', ['class' => 'btn btn-primary'])}}
    {!! Form::close() !!}
@endsection