update sysdata.rda

Author: jgabry

DESCRIPTION

@@ -26,7 +26,7 @@ URL: https://mc-stan.org/bayesplot/
 BugReports: https://github.com/stan-dev/bayesplot/issues/
 SystemRequirements: pandoc (>= 1.12.3), pandoc-citeproc
 Depends:
-    R (>= 3.5.0)
+    R (>= 3.1.0)
 Imports:
     dplyr (>= 0.8.0),
     ggplot2 (>= 3.0.0),