Airbake::Backtrace::Line#method => #method_name
https://github.com/airbrake/airbrake/commit/8768b1c103ac985deee68de10b082b95119c3f35
Merge branch 'airbrake-new-version-support'
Airbake::Backtrace::Line#method has been changed to Line#method_name
since v3.1.9