remove useDevel mention

DESCRIPTION

 Package: splatter
 Type: Package
 Title: Simple Simulation of Single-cell RNA Sequencing Data
-Version: 1.5.5
+Version: 1.5.6
 Date: 2018-08-20
 Author: Luke Zappia
 Authors@R:

index.md

@@ -56,8 +56,7 @@ from Bioconductor:
 
 ```{r}
 library(BiocManager)
-useDevel()
-biocValid()              # checks for out of date packages
+valid()              # checks for out of date packages
 BiocManager::install()               # (optional) updates out of date packages
 BiocManager::install("splatter")
 ```