Fix issue with keys ending to dot '.'

- match_to_key method adds '*' at the end of the key, which makes
  valid_key? to return false, since '*' is not in the list of valid
  characters defined in VALID_KEY_RE
- because the key is invalid, it is ignored
Make @ a valid character in keys

- In Rails views, there might be instance variables, e.g.
  t('payment.status.#{@payment_status}')
Consider keys ending to : as an expression
Merge pull request #90 from sharetribe/dynamic-fix

Dynamic keys are ignored due to the asterisk at the end of the key
Merge pull request #89 from sharetribe/allow-instance-variables

Make @ a valid character in keys
Bump to 0.7.5
Merge remote-tracking branch 'upstream/master'

* upstream/master:
  Bump to 0.7.5
  Consider keys ending to : as an expression
  Make @ a valid character in keys
  Fix issue with keys ending to dot '.'