Mailgun Mail Sending problem

Hi Awesome People

I have been trying to send mail on submitting a form with gmail which din't work so now i created a free mailgun account and tried implementing but i'm facing issues with this too, idk all mail services are angry at me or something

Now i'm Getting the bellow error

RequestException in CurlFactory.php line 187:
cURL error 60: SSL certificate problem: unable to get local issuer certificate (see http://curl.haxx.se/libcurl/c/libcurl-errors.html)

I did installed guzzle by adding "guzzlehttp/guzzle": "~5.3|~6.0" and updated the composer

My Configration in ".env" is

MAIL_DRIVER=mailgun
MAIL_HOST=smtp.mailgun.org
MAIL_PORT=587
MAIL_USERNAME=postmaster@sandbox############.mailgun.org
MAIL_PASSWORD=Mygunpass
MAIL_ENCRYPTION=tls

MAILGUN_DOMAIN=sandbox#############.mailgun.org
MAILGUN_SECRET=key-#####224##########

And In "Service.php"

    'mailgun' => [
        'domain' => env('MAILGUN_DOMAIN'),
        'secret' => env('MAILGUN_SECRET'),
    ],

And My Form is contact.blade.php

  <form method="POST" action="contact" id="contact_form" class="contact-form custm-form" role="form" 
enctype="multipart/form-data">
                    {!! csrf_field() !!}
                    <div class="row">
                      <div class="col-md-6">
                        <ul class="row">
                          <li class="col-sm-12">
                            <label>
                              <input type="text" class="form-control" name="name" id="name" placeholder="Your Name" required>
                            </label>
                          </li>
                          <li class="col-sm-12">
                            <label>
                              <input type="email" class="form-control" name="email" id="email" placeholder="E-Mail" required>
                            </label>
                          </li>
                          <li class="col-sm-12">
                            <label>
                              <input type="number" class="form-control" name="phone" id="phone" placeholder="Phone" required>
                            </label>
                          </li>
                          <li class="col-sm-12">
                            <label>
                              <input type="text" class="form-control" name="subject" id="subject" placeholder="Subject" required>
                            </label>
                          </li>
                        </ul>
                      </div>
                      <div class="col-md-6">
                        <ul class="row">
                          <li class="col-sm-12">
                            <label>
                              <textarea class="form-control" name="message" id="message" rows="5" placeholder="Your Message"></textarea>
                            </label>
                          </li>
                          <li class="col-sm-12">
                            <button type="submit" value="submit" class="btn" id="btn_submit">Send Message</button>
                          </li>
                        </ul>
                      </div>
                    </div>
      </form>

And My Controller is AcoContactController.php

<?php

namespace App\Http\Controllers;

use View;
Use Mail;
use App\AvoContact;
use App\Http\Requests;
use App\Http\Requests\ContactFormRequest;
use Illuminate\Routing\Controller as BaseController;


class AvoContactController extends BaseController {

    public function contactpage()
    {
        $contact = AvoContact::all();

        return view('pages.contact')->with(['contact' => $contact]);
    }

    public function store(ContactFormRequest $request)
    {
        Mail::send('emails.contact', [], function ($m) use($request){
            $m
              ->from(env('MAIL_USERNAME')) // also tried postmaster@sandbox############.mailgun.org
              ->to('sanjiarya2112@gmail.com')
              ->subject('Your Reminder!');
        });

        return 'Email Sent';

    }  

}

And The Route is

Route::get('contact', 'AvoContactController@contactpage');
Route::post('contact', 'AvoContactController@store');

I have Posted all my code, i really can't seem finding what is the issue with sending mail

Looking forward for much needed help

Thank You