py-arrow: updated to 0.15.5

0.15.5:

- [WARN] Python 2 reached EOL on 2020-01-01. arrow will **drop support** for Python 2 in a future release to be decided.
- [NEW] Added bounds parameter to ``span_range``, ``interval`` and ``span`` methods. This allows you to include or exclude the start and end values.
- [NEW] ``arrow.get()`` can now create arrow objects from a timestamp with a timezone, for example:

.. code-block:: python

    >>> arrow.get(1367900664, tzinfo=tz.gettz('US/Pacific'))
    <Arrow [2013-05-06T21:24:24-07:00]>

- [NEW] ``humanize`` can now combine multiple levels of granularity, for example:

.. code-block:: python

    >>> later140 = arrow.utcnow().shift(seconds=+8400)
    >>> later140.humanize(granularity="minute")
    'in 139 minutes'
    >>> later140.humanize(granularity=["hour", "minute"])
    'in 2 hours and 19 minutes'

- [NEW] Added Hong Kong locale (``zh_hk``).
- [NEW] Added ``humanize`` week granularity translation for Dutch.
- [NEW] Numbers are now displayed when using the seconds granularity in ``humanize``.
- [CHANGE] ``range`` now supports both the singular and plural forms of the ``frames`` argument (e.g. day and days).
- [FIX] Improved parsing of strings that contain punctuation.
- [FIX] Improved behaviour of ``humanize`` when singular seconds are involved.

(adam)