Ensure 'try' is called from base package

Fixes a problem where `try` could be called from another environment if overwritten, e.g.

    try <- function(ouch) {}
    plot(1:5)

```R
> try <- function(ouch) {}
> plot(1:5)
Error in try(grDevices:::png("/var/folders/tm/5dt8p5s50x58br1k6wpqnwx00000gn/T//Rtmpk2Fiyj/ef2163cc287e434e82c79182e59586d8.png",  : 
  unused argument (TRUE)
 Show Traceback
 
 Rerun with Debug
 Error in RStudioGD() : 
  Shadow graphics device error: r error 4 (R code execution error) 
```