The encryption_package can now be updated without uninstalling it first

[nicolasriousset]

As detailed in issue #56, the encryption_package couldn't be updated without uninstalling it first.
This was problematic when the functions were used in Vertica column default expression, because dropping a library used by a default expression caused the whole table to be lost.

Solved the issue by using a 'CREATE OR REPLACE' statement instead of a simple 'CREATE'.

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