Bug fix: set ratio between physical units correctly in plotSpatial

[codecov[bot]]

Codecov Report

Patch coverage: 100.00% and no project coverage change.

Comparison is base (736ab56) 99.45% compared to head (69e39fa) 99.45%.

:exclamation: Current head 69e39fa differs from pull request most recent head e2fbec5. Consider uploading reports for the commit e2fbec5 to get more accurate results

Additional details and impacted files

```diff @@ Coverage Diff @@ ## devel #112 +/- ## ======================================= Coverage 99.45% 99.45% ======================================= Files 23 23 Lines 1832 1842 +10 ======================================= + Hits 1822 1832 +10 Misses 10 10 ``` | [Files Changed](https://app.codecov.io/gh/BodenmillerGroup/imcRtools/pull/112?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=BodenmillerGroup) | Coverage Δ | | |---|---|---| | [R/plotSpatial.R](https://app.codecov.io/gh/BodenmillerGroup/imcRtools/pull/112?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=BodenmillerGroup#diff-Ui9wbG90U3BhdGlhbC5S) | `100.00% <ø> (ø)` | | | [R/utils.R](https://app.codecov.io/gh/BodenmillerGroup/imcRtools/pull/112?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=BodenmillerGroup#diff-Ui91dGlscy5S) | `99.38% <100.00%> (+<0.01%)` | :arrow_up: | | [R/validityChecks.R](https://app.codecov.io/gh/BodenmillerGroup/imcRtools/pull/112?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=BodenmillerGroup#diff-Ui92YWxpZGl0eUNoZWNrcy5S) | `99.68% <100.00%> (+<0.01%)` | :arrow_up: |

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