added quotes to filename in load_models

[glenrs]

@mmastand This one should be really quick.

I can't really make a reprex example for this one because it is interactive.

[codecov[bot]]

Codecov Report

Merging #1262 into master will increase coverage by 0.1%. The diff coverage is 100%.

@@           Coverage Diff            @@
##           master   #1262     +/-   ##
========================================
+ Coverage    95.1%   95.2%   +0.1%     
========================================
  Files          40      40             
  Lines        3102    3102             
========================================
+ Hits         2952    2956      +4     
+ Misses        150     146      -4