add a shinytest test for event_data app

Author: cpsievert

.travis.yml

@@ -33,3 +33,6 @@ before_script:
 
 # work around temporary travis + R 3.5 bug
 r_packages: devtools  
+
+# temporary: needed for plotly input testing in shiny 
+r_github_packages: rstudio/shinytest

DESCRIPTION

@@ -54,6 +54,7 @@ Suggests:
     knitr,
     devtools,
     shiny (>= 1.1.0),
+    shinytest (> 1.3.0),
     curl,
     rmarkdown,
     vdiffr,