[Fix] ensure if `npm link` fails, that `$IFS` is not improperly set.

https://github.com/creationix/nvm/issues/1519#issuecomment-297850323

nvm.sh

@@ -3157,6 +3157,7 @@ nvm() {
       nvm_echo "$INSTALLS" | command xargs npm install -g --quiet
 
       nvm_echo "Linking global packages from $VERSION..."
+      (
         set -f; IFS='
 ' # necessary to turn off variable expansion except for newlines
         for LINK in $LINKS; do
@@ -3165,7 +3166,7 @@ nvm() {
             (nvm_cd "$LINK" && npm link)
           fi
         done
-      set +f; unset IFS # restore variable expansion in case $LINKS was empty
+      )
     ;;
     "clear-cache" )
       command rm -f "$NVM_DIR/v*" "$(nvm_version_dir)" 2>/dev/null