Update dependency get_it to v4

[renovate]

This PR contains the following updates:

Package	Type	Update	Change
get_it	dependencies	major	^1.0.3 -> ^4.0.0

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Release Notes

fluttercommunity/get_it

v4.0.4

[4.0.4] - 22.07.2020

• fixed linter errors

v4.0.3

[4.0.3] - 22.07.2020

• fixes of several typos thanks to PRs from @​Bryanx, @​sspatari
• fixed error Issue with reseting lazy Singletone fluttercommunity/get_it#92

v4.0.2

[4.0.2] - 26.04.2020

• removed too strong type check for passed factory parameter
• fixed error message Wrong error message for non-async dependency fluttercommunity/get_it#69

v4.0.1

[4.0.1] - 19.03.2020

• overhauled readme
• removed unnecessary print statement

v4.0.0

[4.0.0] - 26.02.2020

• Added abstract WillSignalReady class

v3.0.1

[3.0.1] - 24.09.2019

• Bugfix with Fix unregister bug when no disposing function provided fluttercommunity/get_it#21

v3.0.0+1

[3.0.0+1] - 07.09.2019

• Small fix to make the analyser happy

v3.0.0

[3.0.0+1] - 07.09.2019

• Small fix to make the analyser happy

v2.1.0

[2.1.0] - 26.08.2019

• Added handy ready signal to make start-up logic a bit easier
• Unregister of Objects now possible with optional disposing function

v2.0.3

[2.0.3] - 26.08.2019

• Small fix

v2.0.1

[2.0.1] - 19.08.2019

• Small fix

v2.0.0

[2.0.0] - 18.08.2019

• Breaking Change with V2.0.0
  you no longer can directly create instances of the type GetIt because GetIt is now a singleton please see README

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