Donation Receipts 2.2.6

Changes since 2.2.5

• [#185] Fix "Undefined index" PHP warnings - by @jensschuppe
• [#186] Fix hook "should be updated to pass an array of parameter names" deprecation notice - by @jensschuppe
• [#187] Fix "Implicit conversion from float to int loses precision" deprecation notice - by @jensschuppe
• [#188] Make "Time Period" field required, but un-require "from" and "to" fields for relative date selections - by @jensschuppe

Full Changelog: 2.2.5...2.2.6