This PR fixes a too greedy regular expression for rake syntax:hiera.

Description:
Given these keys in a common.yaml:

---
firstkey: 'one'
secondkey: 'two'
mymod::mykey: "%{lookup('firstkey')}%{lookup('secondkey')}"

This concatenates the keys 'firstkey' ('one') and 'secondkey' ('two') to 'mykey' ('onetwo').
Because of a too greedy regular expression, this leads to a warning, which shouldn't.

Expected result:

# rake syntax:hiera
---> syntax:hiera:yaml
#

Actual result:

# rake syntax:hiera
---> syntax:hiera:yaml
WARNING: data/common.yaml: Key :mymod::mykey: string after a function call but before `}` in the value
#

Explanation:
The regular expression /%{.+\('.*'\).+}/ matches %{lookup('firstkey')}%{lookup('secondkey')}, which fires the Warning.
The regular expression /%{[^}]+\('[^}]*'\)[^}\s]+}/ does not match %{lookup('firstkey')}%{lookup('secondkey')}.
It still matches %{lookup('firstkey'):3306}%{lookup('secondkey')} or any other non-whitespace character between ) and the next } in a function interpolation, which is the purpose of the Warning.