Bump version number

DESCRIPTION

 Package: splatter
 Type: Package
 Title: Simple Simulation of Single-cell RNA Sequencing Data
-Version: 1.2.0
-Date: 2017-10-13
+Version: 1.2.1
+Date: 2017-11-23
 Author: Luke Zappia
 Authors@R:
     c(person("Luke", "Zappia", role = c("aut", "cre"),

NEWS.md

+## Version 1.2.1 (2017-11-23)
+
+* Fix zinbwave installation error
+
 # Version 1.2.0 (2017-10-30)
 
 * Bioconductor 3.6 release