R API: Change SSLv3 to TLSv1

Yesterday, for security reasons SSLv3 got deprecated. Message returned from running `py$ggplotly()`:
```
Error in function (type, msg, asError = TRUE)  :
  Unknown SSL protocol error in connection to plot.ly:-9824
```

Protocol is changed from SSLv3 to TLSv1. `sslversion=1` is for TLSv1, see http://stackoverflow.com/questions/17119449/rcurl-boolean-options. It can me checked with:
```
c(RCurl:::SSLVERSION_TLSv1, RCurl:::SSLVERSION_SSLv3)
```

cc/ @mkcor