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 @@ class String
     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