Addressing cran failing issues

[juniperlsimonis]

build issue associated with downloading resources for vignette building

Quitting from lines 201-225 [download pre-generated model outputs] (paper-comparison.Rmd) Error: processing vignette 'paper-comparison.Rmd' failed with diagnostics: cannot open URL 'https://raw.githubusercontent.com/weecology/LDATS-replications/master/output/ldats_ldats.RDS' --- failed re-building ‘paper-comparison.Rmd’

converting to precomputing approach following https://ropensci.org/blog/2019/12/08/precompute-vignettes/

also, because this is the first update in a bit, using github actions for replacing travis

[codecov[bot]]

Codecov Report

Patch has no changes to coverable lines.

:exclamation: Current head fb638d8 differs from pull request most recent head 4aefa8a. Consider uploading reports for the commit 4aefa8a to get more accurate results

Files Changed	Coverage
R/LDA.R	ø
R/LDA_TS.R	ø
R/TS.R	ø
R/ptMCMC.R	ø

:loudspeaker: Thoughts on this report? Let us know!.