Allow dashes in database name, simplify regex expression

[bruceharrison1984]

The is a simple one line change that allows for dashes in database name, which Postgres supports. It also simplifies the regex expression to just use the \w operator, since it is equivalent to the existing expression.

^[\w-]*$

^ asserts position at start of a line
\w matches any word character (equivalent to [a-zA-Z0-9_])
- matches the character - with index 4510 (2D16 or 558) literally (case sensitive)
* matches the previous token between zero and unlimited times, as many times as possible, giving back as needed (greedy)
$ asserts position at the end of a line

Would also address this old issue: #663

[zalando-robot]

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