node: add support for npm 7

Co-Authored-By: Mike McQuaid <mike@mikemcquaid.com>

Library/Homebrew/language/node.rb

@@ -44,6 +44,9 @@ module Language
 
       pack = pack_for_installation
 
+      # npm 7 requires that these dirs exist before install
+      (libexec/"lib").mkpath
+
       # npm install args for global style module format installed into libexec
       args = %W[
         -ddd

Library/Homebrew/test/language/node_spec.rb

@@ -25,7 +25,7 @@ describe Language::Node do
   end
 
   describe "#std_npm_install_args" do
-    npm_install_arg = "libexec"
+    npm_install_arg = Pathname("libexec")
     npm_pack_cmd = "npm pack --ignore-scripts"
 
     it "raises error with non zero exitstatus" do