Allow /-/ in MediaWikiVersionFetcher::fetchVersion

Alters MediaWikiVersionFetcher::fetchVersion() so that tests allow
versions to use Semantic Versioning (http://semver.org/)

See I2255ac2999ad207203fa6514f2e1b23f5d7965d7 for the fix in REL1_24

Change-Id: I6e9e154f864e771a02ae1da0e1530afe7f8a4cd0
Merge "Allow /-/ in MediaWikiVersionFetcher::fetchVersion"