Increment version number to 0.4.2.9000

DESCRIPTION

@@ -1,7 +1,7 @@
 Type: Package
 Package: xaringanthemer
 Title: Custom 'xaringan' CSS Themes
-Version: 0.4.2
+Version: 0.4.2.9000
 Authors@R: 
     person("Garrick", "Aden-Buie", , "garrick@adenbuie.com", role = c("aut", "cre"),
            comment = c(ORCID = "0000-0002-7111-0077"))

NEWS.md

@@ -1,3 +1,5 @@
+# xaringanthemer (development version)
+
 <!-- NEWS.md is maintained by https://cynkra.github.io/fledge, do not edit -->
 
 # xaringanthemer 0.4.2