Fix time complexity documentation for insertion of Sequence into Heap

[macbellingrath]

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Description

The documentation of

insert<S: Sequence>(_ sequence: S) where S.Iterator.Element == T

states that the time complexity of this method is O(log n). This is not correct as it calls this method

insert(_ value: T) // time complexity of O(log n)

n times.

The overall complexity is thus O(n log n)