flatten-array: update to v1.1.0 of canonical tests

pig-latin: convert to use instance methods

prime-factors: convert to use instance methods

nth-prime: make use instance method [Fix #358]

https://github.com/exercism/x-common/blob/d7a3c09b6758a8a5d59a2e140e6684031316280a/exercises/flatten-array/canonical-data.json

+ bookstore: add missing import statement in tests

twelve-days: use instance methods [Fix #357]

Beer song instance methods

Fixes issue #357.

Refactoring from static methods to instance methods

sum-of-multiples: use instance method instead of static method [Fix #355]

difference-of-squares: adjust API to use instance method [Fix #253]

Fixes issue #355.

Sieve redundant array

Switched from Arrays.asList to a Collections.singletonList

Fixed issue #359

Fix for issue #354: extract common setup

extracted instance construction to setUp() method.

Extracted construction into setUp() method.

flatten-array: add @Ignore to tests [Fix #379]

Fixes issue #253.

binary-search-tree: remove redundant .keep file [Fix #329]

binary-search: remove redundant .keep file [Fix #328]

Fixes issue #351.

allergies: remove redundant .keep file [Fix #327]

luhn: extract common setup [Fix #356]

robot-name: avoid test pollution [Fix #362]

grade-school: remove potential test pollution [Fix #371]

Wordy extract setup

Make raindrops use instance method