[Robustness] add a missing `command` to a `sed` call

nvm.sh

@@ -999,7 +999,7 @@ nvm_print_implicit_alias() {
       NVM_IOJS_VERSION="$($NVM_COMMAND)"
       EXIT_CODE="$?"
       if [ "_$EXIT_CODE" = "_0" ]; then
-        NVM_IOJS_VERSION="$(nvm_echo "$NVM_IOJS_VERSION" | sed "s/^$NVM_IMPLICIT-//" | command grep -e '^v' | command cut -c2- | command cut -d . -f 1,2 | uniq | command tail -1)"
+        NVM_IOJS_VERSION="$(nvm_echo "$NVM_IOJS_VERSION" | command sed "s/^$NVM_IMPLICIT-//" | command grep -e '^v' | command cut -c2- | command cut -d . -f 1,2 | uniq | command tail -1)"
       fi
 
       if [ "$ZHS_HAS_SHWORDSPLIT_UNSET" -eq 1 ] && nvm_has "unsetopt"; then