Add String#end_with?

I'm tired of not remembering if start_with?/end_with? are portable, so
just add them both if they're not defined.

Library/Homebrew/extend/string.rb

@@ -24,6 +24,15 @@ def start_with?(*prefixes)
  end
  end unless method_defined?(:start_with?)
 
+ def end_with?(*suffixes)
+ suffixes.any? do |suffix|
+ if suffix.respond_to?(:to_str)
+ suffix = suffix.to_str
+ self[-suffix.length, suffix.length] == suffix
+ end
+ end
+ end unless method_defined?(:end_with?)
+
  # String.chomp, but if result is empty: returns nil instead.
  # Allows `chuzzle || foo` short-circuits.
  def chuzzle