bench: fix runner

Author: kgryte

lib/node_modules/@stdlib/math/base/special/erf/benchmark/r/benchmark.R

@@ -99,7 +99,7 @@ main <- function() {
 		results <- microbenchmark::microbenchmark( erf( (2.0*runif(1L)) - 1.0 ), times = iterations );
 
 		# Sum all the raw timing results to get a total "elapsed" time:
-		elapsed <- sum( results[[ time ]] );
+		elapsed <- sum( results[[ 'time' ]] );
 
 		# Convert the elapsed time from nanoseconds to seconds:
 		elapsed <- elapsed / 1.0e9;