add ggplot2 loading to visc_empty skeleton.Rmd

[kelliemac]

Description

add ggplot2 loading to visc_empty skeleton.Rmd

Related Issues

addresses #251

Checklist

• This PR includes unit tests
• This PR establishes a new function or updates parameters in an existing function
  • The roxygen skeleton for this function has been updated using devtools::document
• I have updated NEWS.md to describe the proposed changes

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 81.79%. Comparing base (b8969f4) to head (112d4a8).
Report is 16 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #256      +/-   ##
===========================================
- Coverage    82.10%   81.79%   -0.32%     
===========================================
  Files            8        8              
  Lines          352      346       -6     
===========================================
- Hits           289      283       -6     
  Misses          63       63              

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[kelliemac]

@slager can you review this PR?

[slager]

Approved, but noticed typo in skelton

[slager]

Resolves #251