Fixes the PurchasesDelegate being deallocated on iOS #362

Job	Run time
test-public-api	1m 46s
test-public-api	20m 36s
validate-binary-compatibility	20m 0s
validate-binary-compatibility	20m 0s
detekt	41s
detekt	41s
test-unit-tests	16m 33s
test-unit-tests	16m 33s
build	0s
build	27m 0s
	2h 3m 50s

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