I have created migration file in that i have written :
public function up()
    {
        //
        Schema::create('ad_group', function (Blueprint $table) {
            $table->increments('id');
            $table->integer('campaign_id')->unsigned();
            $table->char('name',32);
        });
        Schema::table('ad_group',function (Blueprint $table){
            $table->foreign('campaign_id')->references->('id')->on('campaigns');
        });
    }
which returns error like this :
[Symfony\Component\Debug\Exception\FatalThrowableError]
  Parse error: syntax error, unexpected '(', expecting identifier (T_STRING) or variable (T_VARIABLE) or '{' or '$' 
 
     
    