Log Message:
Update textproc/erlang-fast_xml to 1.1.15.

Version 1.1.15
- Update to p1_utils 1.0.5

Version 1.1.14
- Erlang OTP R19 compliance
- Fix compilation on rebar3

Version 1.1.13
- Use p1_utils 1.0.4

Version 1.1.12
- Generator improvements

Version 1.1.11
- Now properly includes Elixir lib/ directory in hex.pm package

Version 1.1.10
- Split build in two steps to fix link step on Ubuntu
- Clean Makefile.mix to remove duplicated code

Version 1.1.9
- Fix Linux build with Mix

Version 1.1.8
- Package priv/lib structure to make sure everything is properly
  build by mix

Version 1.1.7
- Fix indent issue in Mix Makefile

Version 1.1.6
- Add missing Makefile.mix file in rebar hex.pm package
  description
- Make sure priv dir is created when building with mix and
  included in package dir list

Version 1.1.4
This is an Elixir friendly update:
- Add ability to return maps instead of xmlel record
- Add ability to tell parser to return Elixir structs instead of
  records
- Add Elixir tests