install.sh: print out tar version when the flag is supported (npm#154)

not all the tar implementations support --version flag
e.g. the one used in openbsd doesn't, so the installation process fails

PR-URL: npm#154
Credit: @agudulin
Reviewed-By: @zkat

scripts/install.sh

@@ -98,8 +98,10 @@ fi
 
 if [ $ret -eq 0 ] && [ -x "$tar" ]; then
   echo "tar=$tar"
-  echo "version:"
-  $tar --version
+  if [ $tar --version > /dev/null 2>&1 ]; then
+    echo "version:"
+    $tar --version
+  fi
   ret=$?
 fi