* develop:
  Bump version to `2.2.3`
  Fix regexp for numeric domains (fixes #72)
  Add `EmailValidator::Error` class, raise `EmailValidator::Error` when invalid `mode`
  Add checks for double dash in domain
  Fix specs for numeric-only domains labels
  Add checks for numeric-only TLDs in tests
  Add tests to ensure that `regexp` returns expected value
  Bump y18n from 3.2.1 to 3.2.2
  Add failing test: strict mode should accept numbers only domains
  Update .travis.yml