Fix some typo in method names, variables
compatability => compatibility
Merge pull request #10761 from vipulnsward/fix-typo-1

Fix some typo in method names, variables
Merge pull request #10762 from vipulnsward/change_compatibility

compatability => compatibility
add test-case for `Array#to_sentence with blank items.
Merge pull request #10763 from senny/10758_to_sentence_with_blank_elements

test-case for `Array#to_sentence` with `blank?` items.