If you're using FactoryGirl, replace all occurrences of 'create' with 'build' and 'git add' the specs that still pass.

dankify_specs.sh

#!/bin/bash

find spec -iname "*spec.rb" -exec sed -i.bak 's/create/build/g' {} \;

find spec -iname "*spec.rb" -print0 | while IFS= read -r -d $'\0' spec; do
  spring rspec $spec --fail-fast
  if [[ $? -gt 0 ]]; then
    echo "$spec did not pass"
  else
    echo "$spec passed!!!"
    git add $spec
  fi
done

If you use parentheses, e.g. create(:thing), you can make the sed command a little more reliable by including a few extra characters:
find spec -iname "*spec.rb" -exec sed -i.bak 's/create(:/build(:/g' {} \;