Update ruby-mustermann to 1.1.1.
Mustermann 1.1.1 (2020-01-04)
* Make sure that requireing ruby2_keywords when needed. Fixes#102 @Annih
Mustermann 1.1.0 (2019-12-30)
* Proper handling of Mustermann::ExpandError. Fixes#88 @namusyaka
* Support Ruby 3 keyword arguments. @mame
o At the same time, we dropped a support that accepts options
followed by mappings on Mustermann::Mapper. Reference commit
* Improve documentation and development. @horaciob, @epistrephein,
@jbampton, @jkowens, @junaruga
a88e891b6c