Make sure `nvm clear-cache` clears the versions directory as well.

nvm.sh

diff --git a/nvm.sh b/nvm.sh
index 9e13892..6e9da50 100644
--- a/nvm.sh
+++ b/nvm.sh
@@ -782,7 +782,7 @@
       npm install -g --quiet $INSTALLS
     ;;
     "clear-cache" )
-      rm -f $NVM_DIR/v* 2>/dev/null
+      rm -f $NVM_DIR/v* "$(nvm_version_dir)" 2>/dev/null
       echo "Cache cleared."
     ;;
     "version" )