Update dependency doctrine/collections to v2

[renovate[bot]]

This PR contains the following updates:

Package	Type	Update	Change
doctrine/collections (source)	require	major	^1.6 -> ^2.0

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Release Notes

doctrine/collections

### [`v2.0.1`](https://togithub.com/doctrine/collections/releases/tag/2.0.1) [Compare Source](https://togithub.com/doctrine/collections/compare/2.0.0...2.0.1) ##### Release Notes for [2.0.1](https://togithub.com/doctrine/collections/milestone/23) 2.0.x bugfix release (patch) ##### 2.0.1 - Total issues resolved: **0** - Total pull requests resolved: **2** - Total contributors: **2** ##### Bug,Static Analysis - [340: Mark closure arguments as always-provided](https://togithub.com/doctrine/collections/pull/340) thanks to [@​greg0ire](https://togithub.com/greg0ire) ##### Documentation - [338: Fix markup](https://togithub.com/doctrine/collections/pull/338) thanks to [@​xepozz](https://togithub.com/xepozz) ### [`v2.0.0`](https://togithub.com/doctrine/collections/releases/tag/2.0.0) [Compare Source](https://togithub.com/doctrine/collections/compare/1.8.0...2.0.0) ##### Release Notes for [2.0.0](https://togithub.com/doctrine/collections/milestone/5) ##### 2.0.0 - Total pull requests resolved: **12** - Total contributors: **9** ##### Types - [332: Add missing param type declarations](https://togithub.com/doctrine/collections/pull/332) thanks to [@​greg0ire](https://togithub.com/greg0ire) - [312: Stop returning true from Collection::add()](https://togithub.com/doctrine/collections/pull/312) thanks to [@​greg0ire](https://togithub.com/greg0ire) - [192: \[2.0\] Strict types, native parameter & return types ](https://togithub.com/doctrine/collections/pull/192) thanks to [@​jwage](https://togithub.com/jwage) ##### Static Analysis - [330: Make Selectable template covariant](https://togithub.com/doctrine/collections/pull/330) thanks to [@​greg0ire](https://togithub.com/greg0ire) - [185: Update Collection::filter docblock to add key parameter to closure](https://togithub.com/doctrine/collections/pull/185) thanks to [@​nicholasruunu](https://togithub.com/nicholasruunu) ##### Improvement - [252: \[2.0\] Add new methods Collection::findFirst and Collection::reduce](https://togithub.com/doctrine/collections/pull/252) thanks to [@​VincentLanglet](https://togithub.com/VincentLanglet) - [176: Preserve keys in ArrayCollection for Criteria firstresults/maxresults](https://togithub.com/doctrine/collections/pull/176) thanks to [@​SenseException](https://togithub.com/SenseException) - [100: Allow use array and multi arguments](https://togithub.com/doctrine/collections/pull/100) thanks to [@​vlastv](https://togithub.com/vlastv) ##### Internal - [197: Upgrade to PHPUnit 8.](https://togithub.com/doctrine/collections/pull/197) thanks to [@​jwage](https://togithub.com/jwage) - [215: Enhancement: improve test suite](https://togithub.com/doctrine/collections/pull/215) thanks to [@​BackEndTea](https://togithub.com/BackEndTea) ##### Bugfixes - [189: Fix return type of Collection::key()](https://togithub.com/doctrine/collections/pull/189) thanks to [@​enumag](https://togithub.com/enumag) ##### Documentation - [187: Documentation for serialization of collections](https://togithub.com/doctrine/collections/pull/187) thanks to [@​SenseException](https://togithub.com/SenseException)

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