Update CHANGELOG.md

"Resolved Issues" title moved on top of resolved issues list in 3.0.18 changelog
Support int keys when using dot notation on read.

[ fix #2740 ]
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Integer deserialization properly casts to integers.

[ fix #2739 ]
Fix #2755: Positional operator update broken for > 10 objects.
Spec reformatting
Update travis yml
create_indexes should not fail when cannot constantize class [Fix #2758]

rake task db:mongoid:create_indexes should not fail if the name of the
file doest not match the class name
Use positional operator across the board.

See the notes in the Mongoid::Atomic::Positionable module - this now
appropriately processes the update operations at persistence time and
makes the necessary adjustments.

[ fix #2745 ]
[ fix #2735 ]
[ fix #2769 ]
[ fix #2770 ]
Ensure positional operator use in embedded inserts.

[ fix #2769 ]
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Merge branch 'pr/2768'
Jruby build should run
Enumerable.matching_document _unloaded double query fix

When there was a many to many, and the target was not loaded and target.first was called, _unloaded was calling the db twice in order to load
Dont clear persistence_options when _loading_revision [ Fixes #2743]
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Update travis with max size
 should support _ids of type hash, array etc.
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Remove c extension opts