title: foreign key is not working when I migrate
body: <p>Foreign key is not working.</p>
  
  <p>This is my migration file</p>
  
  <pre><code>Schema::create('course_prospect', function (Blueprint $table) {
        $table-&gt;bigIncrements('id');
  
        $table-&gt;integer('prospect_id')-&gt;length(11)-&gt;unsigned();
        $table-&gt;foreign('prospect_id')-&gt;references('id')-&gt;on('prospect');
  
        $table-&gt;integer('course_id')-&gt;length(11)-&gt;unsigned();
        $table-&gt;foreign('course_id')-&gt;references('course_id')-&gt;on('course');
  
        $table-&gt;timestamps();
      });
  </code></pre>
  
  <p>I'm getting this error</p>
  
  <pre><code> Illuminate\Database\QueryException  : SQLSTATE[HY000]: General error: 
  1005 Can't create table `customerinquirydb`.`#sql-104c_e9` (errno: 150 
  "Foreign key constraint is incorrectly formed") (SQL: alter table 
  `course_prospect` add constraint `course_prospect_prospect_id_foreign` 
  foreign key (`prospect_id`) references `prospect` (`id`))
  </code></pre>