flowEnd: do not print unnecessary OK
flowEnd: do not print unnecessary OK

The instrument task now print a summary line and the "OK" at the end
of each file can be removed. Verbose output now looks like:

  Running "instrument" task
  Verifying property instrument.files exists in config...OK
  Options: basePath="coverage/instrumented", flatten=false, lazy
  Reading app/js/app.js...OK
  Writing coverage/instrumented/app/js/app.js...OK
  Reading app/js/auth.js...OK
  Writing coverage/instrumented/app/js/auth.js...OK
  Instrumented 2 files (skipped 9 files)

  Done, without errors.

and normal output looks like:

  Running "instrument" task
  Instrumented 2 files (skipped 9 files)

  Done, without errors.

acvetkov/grunt-istanbul,MailOnline/grunt-istanbul,taichi/grunt-istanbul