fix(script): fix output redirection for resolv.conf update

From the bash man page:

  Note that the order of redirections is significant. For example, the
  command

    ls > dirlist 2>&1

  directs both standard output and standard error to the file dirlist,
  while the command

    ls 2>&1 > dirlist

  directs only the standard output to file dirlist, because the standard
  error was duplicated from the standard output before the standard
  output was redirected to dirlist.

I changed this to &> which redirects both stdout and stderr to the same
file.
fix(hosts): update sed expression to work with BSD sed

BSD sed is used on OS X. This version of sed requires an argument to be
passed together with the -i flag. Bash interprets -i'' and -i the exact
same way (this is how string concatenation works in Bash), so the space
is required for sed to notice the empty flag.