Add NVM_DIR to install, minor edits to nvm item

functions/_tide_item_nvm.fish

@@ -1,6 +1,6 @@
 function _tide_item_nvm
     if set -l whichNode (which node 2>/dev/null) # Ensure node is installed
-        set -l nodeVersion (node --version)
+        set -l nodeVersion (string split / $whichNode)[-3] # Much faster than node --version
 
         if test -n "$tide_nvm_default_node"
             if test "$tide_nvm_default_node" != "$nodeVersion"

tools/_tide_actual_install.fish

@@ -75,6 +75,7 @@ function _set_immutables
     _set_immutable _tide_color_normal (set_color normal)
 
     _set_immutable VIRTUAL_ENV_DISABLE_PROMPT true
+    _set_immutable NVM_DIR $HOME/.nvm
 end
 
 function _set_immutable -a var_name