Symfony\Component\Debug\Exception\FatalThrowableError | Undefined function string()

I'm trying to use the command php artisan migrate but my problem arises when I get the following error from Symfony [Symfony\Component\Debug\Exception\FatalThrowableError] Call to undefined function string(). I do have the mbstring extension installed. I'm not sure if it matters but I'm running php 7.0.6, mysql 5.5.49-log, & mysqli for my extension.

Here is my migration file:

<?php

use Illuminate\Database\Schema\Blueprint;
use Illuminate\Database\Migrations\Migration;

class CreateUsersTable extends Migration
{
    /**
     * Run the migrations.
     *
     * @return void
     */
    public function up()
    {
        Schema::create('users', function (Blueprint $table) {
            $table->increments('id');
            $table->timestamps();
            $table->string('email');
            $table->string('first_name');
            $table-string('last_name');
            $table->string('user_name');
            $table->string('password');
            $table->rememberToken();
        });
    }

    /**
     * Reverse the migrations.
     *
     * @return void
     */
    public function down()
    {
        Schema::drop('users');
    }
}

via Chebli Mohamed