Update git submodules

* Update yaml2ical from branch 'master'
  - Add DTSTAMP and UID values to meeting instances
    
    The iCalendar spec expects a meeting vEvent to include a datetime stamp
    and a unique ID for each instance. This adds these values to the
    generated output.
    
    Minor cleanup also included since I was touching code around them and
    noticed little nits.
    
    Change-Id: I4753571850665a2f28a6799b84ead4c31a275cc7
    Signed-off-by: Sean McGinnis <sean.mcginnis@gmail.com>
    
  - OpenDev Migration Patch
    
    This commit was bulk generated and pushed by the OpenDev sysadmins
    as a part of the Git hosting and code review systems migration
    detailed in these mailing list posts:
    
    http://lists.openstack.org/pipermail/openstack-discuss/2019-March/003603.html
    http://lists.openstack.org/pipermail/openstack-discuss/2019-April/004920.html
    
    Attempts have been made to correct repository namespaces and
    hostnames based on simple pattern matching, but it's possible some
    were updated incorrectly or missed entirely. Please reach out to us
    via the contact information listed at https://opendev.org/ with any
    questions you may have.
    
  - add day_specifier to recurrence
    
    Add a new property to the recurrence that can be used to generate
    grammatically correct versions of phrases like 'Monthly on the first
    Thursday'.
    
    Change-Id: I2ebfd60ebfbbc499ed08f6f63e91cbb87c8691b1
    Signed-off-by: Doug Hellmann <doug@doughellmann.com>
    
  - add base class for recurrence
    
    Add an abstract base class for the recurrence rules so it is clear
    which methods are required.
    
    Change-Id: I7f2395bf3073b205a280d05f7f844f43a0e85ded
    Signed-off-by: Doug Hellmann <doug@doughellmann.com>
    
  - update the versions of python 3 claimed
    
    We're running at least 3.5 in CI, so start there.
    
    Update tox to set the environments from newest to oldest to avoid
    issues with the dbm format selected for the .testrepository database
    generated by the tests, to allow it to work for all tox environments
    on a local system.
    
    Change-Id: I7cde15039f782bba69ed9e0e44b08e289148019e
    Signed-off-by: Doug Hellmann <doug@doughellmann.com>
    
  - add monthly recurrence options
    
    Add a recurrence option for meetings that repeat monthly. Instantiate
    the ones for the first weekdays of the month for now.
    
    Change-Id: I0fa95653594dc5a28008630f57bee67b92537d29
    Signed-off-by: Doug Hellmann <doug@doughellmann.com>
    
  - fix tox python3 overrides
    
    We want to default to running all tox environments under python 3, so
    set the basepython value in each environment.
    
    We do not want to specify a minor version number, because we do not
    want to have to update the file every time we upgrade python.
    
    We do not want to set the override once in testenv, because that
    breaks the more specific versions used in default environments like
    py35 and py36.
    
    Change-Id: I87982923ab6ecda0673008070da6880536783b40
    
  - Fix output used by http://eavesdrop.openstack.org
    
    Closes-Bug: #1771365
    
    Change-Id: Ib2f695a0b36f704b85f9078b34c9811509906b6d
    Signed-off-by: Graham Hayes <gr@ham.ie>
    
  - Document new quadweekly frequencies
    
    While doing so move the frequency description out of line into it's own
    section.
    
    Change-Id: If757d7192e41d29c0013c46fcda16e44e2f58aa1
    Co-Authored-By: Graham Hayes <gr@ham.ie>
    
  - Allow for meeting to be scheduled every 4 weeks.
    
    This allows for by weekly meetings to be run at alternate
    times.
    
    Change-Id: Ief437e53719c123399de8874469ef16540d3b3fd
    Signed-off-by: Graham Hayes <gr@ham.ie>

yaml2ical

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-Subproject commit 2bc859072ffd3a6687084f98ab356bcaff27c830
+Subproject commit a63d1c5e122a3ee6622be46c64915bd2df1afc37