R 3.5.1 is released few months ago. We better test higher versions of R in AppVeyor.
R 3.6.0 is released 2019-04-26. This PR targets to change R version from 3.5.1 to 3.6.0 in AppVeyor.
We should set `R_REMOTES_NO_ERRORS_FROM_WARNINGS` to `true` to avoid the warnings below:
Error in strptime(xx, f, tz = tz) :
(converted from warning) unable to identify current timezone 'C':
please set environment variable 'TZ'
Error in i.p(...) :
(converted from warning) installation of package 'praise' had non-zero exit status
Calls: <Anonymous> ... with_rprofile_user -> with_envvar -> force -> force -> i.p
This JIRA targets to the latest of R version 3.6.0.