GitLab

* Update docs for Imputer class

* Throw exception when trying to transform imputer without train data

* Update changelog

* tests: update to PHPUnit 6.0 with rector

* fix namespaces on tests

* composer + tests: use standard test namespace naming

* update travis

* resolve conflict

* phpstan lvl 2

* phpstan lvl 3

* phpstan lvl 4

* phpstan lvl 5

* phpstan lvl 6

* phpstan lvl 7

* level max

* resolve conflict

* [cs] clean empty docs

* composer: bump to PHPUnit 6.4

* cleanup

* composer + travis: add phpstan

* phpstan lvl 1

* composer: update dev deps

* phpstan fixes

* update Contributing with new tools

* docs: link fixes, PHP version update

* composer: drop php-cs-fixer, cs already handled by ecs

* ecs: add old set rules

* [cs] apply rest of rules

* upgrade to PHP 7.1

* bump travis and composer to PHP 7.1

* fix tests