Stable library version for citationStyles

[chriba]

The last stable version was in 13-Sep-2013 (according to MavenCentral) and they contain only the old 1.0 CitationStyles.

For the new v1.0.1 CitationStyles we have to use the snapshots (for now, I asked in the official CitationStyles repo for a stable release citation-style-language/styles#2221)

Important for PR: #1928

[koppor]

The usage of SNAPSHOT is intentional by the developers (see citation-style-language/styles#2221 (comment)): They ensure that this artifact always includes all citation styles. Further, they have quality control in place ensuring that nothing breaks at SNAPSHOT (citation-style-language/styles#2221 (comment)). So it is OK to keep SNAPSHOT.

Note: This is only the dependency containing the citation styles. Not the library used for transformation. For that library, a stable version is used.