Increment the cache.

Who wants to place their bets on the final cache value
when we hit SM5 final?

src/Song.cpp

@@ -41,7 +41,7 @@
  * @brief The internal version of the cache for StepMania.
  *
  * Increment this value to invalidate the current cache. */
-const int FILE_CACHE_VERSION = 187;
+const int FILE_CACHE_VERSION = 188;
 
 /** @brief How long does a song sample last by default? */
 const float DEFAULT_MUSIC_SAMPLE_LENGTH = 12.f;