ASV: fix params to be strings (for better repr)
Small fix to using params in asv (otherwise the name was huge, list of 500000 elements)

cc @gfyoung (just so you know I changed this for future reference)

## [Current coverage](https://codecov.io/gh/pydata/pandas/pull/13805?src=pr) is 85.23% (diff: 100%)

> Merging [#13805](https://codecov.io/gh/pydata/pandas/pull/13805?src=pr) into [master](https://codecov.io/gh/pydata/pandas/branch/master?src=pr) will not change coverage

``` diff
@@             master     #13805   diff @@
==========================================
  Files           140        140          
  Lines         50415      50415          
  Methods           0          0          
  Messages          0          0          
  Branches          0          0          
==========================================
  Hits          42970      42970          
  Misses         7445       7445          
  Partials          0          0          
```

> Powered by [Codecov](https://codecov.io?src=pr). Last update [8f64ad7...06a5fa4](https://codecov.io/gh/pydata/pandas/compare/8f64ad700bb254e17fdb006b08199a2cc6ee5f36...06a5fa4123e15340a9b9917d1fb339b5e8503e45?src=pr)
