Fixed deprecation warnings while Nim compiles.

I just removed unsigned and changed a writeLn() call to writeLine() to
avoid the remaining deprecation warnings.

lib/pure/nativesockets.nim

@@ -12,7 +12,7 @@
 
 # TODO: Clean up the exports a bit and everything else in general.
 
-import unsigned, os
+import os
 
 when hostOS == "solaris":
   {.passl: "-lsocket -lnsl".}