Laravel 迁移：外键约束格式不正确(errno 150)

When migrating my DB, this error appears. Below is my code followed by the error that I am getting when trying to run the migration.

Code

public function up()
{
    Schema::create('meals', function (Blueprint $table) {
        $table->increments('id');
        $table->integer('user_id')->unsigned();
        $table->integer('category_id')->unsigned();
        $table->string('title');
        $table->string('body');
        $table->string('meal_av');
        $table->timestamps();
        $table->foreign('user_id')
            ->references('id')
            ->on('users')
            ->onDelete('cascade');
        $table->foreign('category_id')
            ->references('id')
            ->on('categories')
            ->onDelete('cascade');
    });
}  

Error message

[Illuminate\Database\QueryException]
SQLSTATE[HY000]: General error: 1005 Can't create table meal.#sql-11d2_1 4 (errno: 150 "Foreign key constraint is incorrectly formed") (SQL: alter
table meals add constraint meals_category_id_foreign foreign key (category_id) references categories (id) on delete cascade)