Heads-up: next merge day is Aug 2

[Francesco Lodolo [:flod]]

Hi,
There is a change of plan for this release cycle, and it impacts
localization: next merge day is going to happen on Aug 2 (next
Wednesday), instead of Aug 7. On Aug 2 strings will move from
l10-central to mozilla-beta.

This change is to ensure that code gets stabilized on the beta branch
before releasing Beta 1. This is likely going to happen from now on in
all cycles, but the modality and dates might change depending on the
results of this first iteration.

Note that cross-channel (targeting merge day for 57 at this point) will
make this kind of changes irrelevant for l10n, since only one repository
would be exposed, containing strings for all branches.

Francesco