Properly handle project names with dashes

[dluksza]

Currenlty lein-git-version plugin will not properly work with projects that have dash in its name. It will generate version.clj file in wrong directory, eg. when project name is 'my-proj' then plugin will generate version.clj file in src/my-proj/version.clj, causing compilation failure. In this case file should be generated in src/my_proj/.