Make cmap_name the colormap for scale_color_cmap_d

[adunmore]

Fixes #691

Updated to same behavior as scale_color_cmap

[codecov[bot]]

Codecov Report

Patch and project coverage have no change.

Comparison is base (2405442) 0.00% compared to head (c4993e3) 0.00%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #693 +/- ## ===================================== Coverage 0.00% 0.00% ===================================== Files 165 165 Lines 10666 10666 ===================================== Misses 10666 10666 ``` | [Impacted Files](https://app.codecov.io/gh/has2k1/plotnine/pull/693?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Hassan+Kibirige) | Coverage Δ | | |---|---|---| | [plotnine/scales/scale\_color.py](https://app.codecov.io/gh/has2k1/plotnine/pull/693?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Hassan+Kibirige#diff-cGxvdG5pbmUvc2NhbGVzL3NjYWxlX2NvbG9yLnB5) | `0.00% <0.00%> (ø)` | |

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[has2k1]

@adunmore, Thank you.