require most recent ggplot2 CRAN release

Author: cpsievert

DESCRIPTION

@@ -22,7 +22,7 @@ URL: https://plot.ly/r, https://cpsievert.github.io/plotly_book/, https://github
 BugReports: https://github.com/ropensci/plotly/issues
 Depends:
     R (>= 3.2.0),
-    ggplot2 (> 2.2.1)
+    ggplot2 (>= 3.0.0)
 Imports:
     tools,
     scales,