update dataobject.md

fixex typo
BUG Fixed critical issue with Folder::find_or_make failing to handle invalid filename characters
BUG Fix UploadField duplicate checking with invalid folderName
Merge pull request #2882 from sanjaymundhra/patch-4

update dataobject.md
DOC: DropdownField __construct

Current docs make PHPStorm spew errors about data types.

`new CheckboxSetField('Countries'...);`

Causes `Expected The, got string`.

Simple restructure.
Merge pull request #2883 from TomSpeak/patch-1

DOC: DropdownField __construct
DOC: SapphireTest `objFromFixture`

The current docs for `objFromFixture` cause PHPStorm to generate an error because of the mismatched data types.

`$product = $this->objFromFixture('ProductPage', 'StandardSpecs');`

Causes: `Expected The, got string`.
Merge pull request #2878 from tractorcow/pulls/fix-folder-find-illegalpath

BUG Fixed critical issue with Folder::find_or_make failing to handle invalid filename characters
Merge pull request #2884 from TomSpeak/patch-2

DOC: SapphireTest `objFromFixture`
Added 3.1.3-rc2 changelog
Adding defaults for unhandled event priorities in log formatters.

Unhandled types wouldn't show up in the error format message, and a
notice "undefined $errtype" is displayed on these cases.
Merge pull request #2892 from silverstripe/log_formatter_defaults

Adding defaults for unhandled event priorities in log formatters.
FIX: getMessageFromSession returning null on first access