code: public function unsigned()
      {
          switch ($this->type) {
              case Schema::TYPE_PK:
                  $this->type = Schema::TYPE_UPK;
                  break;
              case Schema::TYPE_BIGPK:
                  $this->type = Schema::TYPE_UBIGPK;
                  break;
          }
          $this->isUnsigned = true;
          return $this;
      }
docs: Marks column as unsigned.
  @return $this
  @since 2.0.7