Update book.bib for Shapiro et al 2021

[kweav]

Add this URL: url={https://github.com/AlexsLemonade/training-modules/blob/48b31640d592dc070f0dba6395695ef78f3dfb4a/RNA-seq/01-qc_trim_quant.Rmd}

Issue originally noted by Katie Miller