if fixes for no match and nil value

[jqr]

Updates the if statement to fix:

• if statements return all arguments on no matching conditions #41 by explicitly returning nil and not defaulting to the return of each_slice.
• if statements return first condition on nil value #42 by better detection of else values which is not dependent on the value being passed.

Also a minor fix to the open-uri use for the latest(?) API.

This change causes 4 failing tests from the test suite cases provided by http://jsonlogic.com/tests.json to all pass:

  1) Failure:
JSONLogicTest#test_170 [test/json_logic_test.rb:20]:
{"if":[false,"apple",false,"banana"]} (data: null).
Expected [false, "apple", false, "banana"] to be nil.

  2) Failure:
JSONLogicTest#test_125 [test/json_logic_test.rb:20]:
{"if":[]} (data: null).
Expected [] to be nil.

  3) Failure:
JSONLogicTest#test_175 [test/json_logic_test.rb:20]:
{"if":[false,"apple",false,"banana",false,"carrot"]} (data: null).
Expected [false, "apple", false, "banana", false, "carrot"] to be nil.

  4) Failure:
JSONLogicTest#test_130 [test/json_logic_test.rb:20]:
{"if":[false,"apple"]} (data: null).
Expected [false, "apple"] to be nil.

[scalp42]

@bhgames any chance to see this merged?