Disabled unused variable warnings

Replaced -Wunused-value warning ignore with -Wunused-variable ignore,
which solves warning with (Apple LLVM version 4.2 (clang-425.0.28)
(based on LLVM 3.2svn))
Merge pull request #6 from maniak-dobrii/semver-1.x

[FIX} Replace `-Wunused-value` with -Wunused-variable. (maniak-dobrii)