Bump version to 1.21.3 in DESCRIPTION file

Author: tonywu1999

DESCRIPTION

@@ -1,6 +1,6 @@
 Package: MSstatsConvert
 Title: Import Data from Various Mass Spectrometry Signal Processing Tools to MSstats Format
-Version: 1.21.2
+Version: 1.21.3
 Authors@R: c(
   person("Mateusz", "Staniak", email = "mtst@mstaniak.pl", role = "aut"),
   person("Devon", "Kohler", email = "kohler.d@northeastern.edu", role = "aut"),