Avoid String#chr

[onk]

Supporting Ruby 1.8 has been dropped. #216

In Ruby 1.9+, string[nth] returns String. No need to call String#chr.

---

FYI:

String#chr is only for compatibility with Ruby 1.8.

• In Ruby 1.8
  • string[nth] returns Integer|nil
  • Use Integer#chr for gets character
• In Ruby 1.9
  • string[nth] returns String|nil
  • String#chr has been implemented to work with the same code as Ruby 1.8

# This code can get char in both 1.8 and 1.9
'foo'[0].chr
# => "f"