Description:
------------
When emitting a string that matches the format \d(:\d)+, (e.g. 1:0) it should be 
quoted, as an unquoted scalar of this type is actually representing an integer in 
base 60 according to the documentation at http://yaml.org/type/int.html.



Test script:
---------------
$yaml_string = <<<YAML
---
node: '1:0'
YAML;

echo yaml_emit(yaml_parse($yaml_string));

Expected result:
----------------
---
node: '1:0'

Actual result:
--------------
---
node: 1:0