unused connection warning when using parse_stream()

[abuchmueller]

> z <- parse_stream("fromUK.json")
opening fileoldClasskRp.connection input connection.
 Found 2918 records...closing fileoldClasskRp.connection input connection.
 Imported 22015 records. Simplifying...
Warning message:
In .Internal(gc(verbose, reset, full)) :
  closing unused connection 3 (/var/folders/s0/sjz6vgxj7fj2x6dqx1pcyys00000gn/T//RtmpYrobz9/filed5c61b7051d)

parse_stream() leaves the connection open after parsing and R issues a connection warning. This not really a useful warning and should be fixed by closing the connection properly after read in the data.