Fix single quote and percent character in PGCRYPTO_KEY

[khattori]

Fixes #319

[coveralls]

Pull Request Test Coverage Report for Build 1292

• 6 of 6 (100.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 100.0%

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Totals
Change from base Build 1288:	0.0%
Covered Lines:	149
Relevant Lines:	149

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💛 - Coveralls

[peterfarrell]

@khattori Thanks for the PR. I'm slightly concerned about all the hoop jumping we are going through to get things properly formatted between ' and % etc.

I am now convinced we should be using Postgres Dollar Quoting and let the DB handle any issues with the string constants:

https://www.postgresqltutorial.com/dollar-quoted-string-constants/

Let's use $pgcrypto$ as our tag.