chore: manually update wellmapr version

I think the reason why this wasn't automatically updated is that I was
using an old version of semantic release (7.2.0 instead of 7.2.1).  I
upgraded to 7.4.0 in the previous commit, so hopefully this won't be a
problem in the future.

wellmapr/DESCRIPTION

@@ -1,6 +1,6 @@
 Package: wellmapr
 Title: File format for 96-well plate layouts
-Version: 1.0.0
+Version: 2.0.0
 Authors@R: as.person(c(
   "Kale Kundert <kale@thekunderts.net> [aut, cre]"
   ))