language/node: npm pack ignore prepublish scripts

This tells npm pack to don't run prepublish scripts at all.
I think this is the best default because:
* most modules don't have a prepublish script at all and aren't affected
  by this change
* most prepublish scripts are calling devDeps, which would fail in our
  case, because (dev)Deps aren't installed at npm pack time until #2820
  gets resolved
* we favor npm registry tarball for formula downloads, which are already
  prepublished, so we would in the best case needlessly run prepublish
  a second time and in the worst case it would fail (because a clean
  step is required before running prepublish a second time in a row)
* This change does the right thing for >99% of all the packages and
  would only affect packages with prepublish scripts downloaded from a
  non-npm registry tarball (like github tarballs) and with a prepublish
  script wich does no't require any devDep (unlike for cross platform)

Library/Homebrew/language/node.rb

@@ -10,7 +10,7 @@ module Language
       # fed to `npm install` only symlinks are created linking back to that
       # directory, consequently breaking that assumption. We require a tarball
       # because npm install creates a "real" installation when fed a tarball.
-      pack_cmd = "npm pack -ddd"
+      pack_cmd = "npm pack -ddd --ignore-scripts"
       ohai pack_cmd
       output = `#{pack_cmd}`
       if !$CHILD_STATUS.exitstatus.zero? || output.lines.empty?

Library/Homebrew/test/language/node_spec.rb

@@ -24,7 +24,7 @@ describe Language::Node do
 
   describe "#std_npm_install_args" do
     npm_install_arg = "libexec"
-    npm_pack_cmd = "npm pack -ddd"
+    npm_pack_cmd = "npm pack -ddd --ignore-scripts"
 
     it "raises error with non zero exitstatus" do
       allow(Language::Node).to receive(:`).with(npm_pack_cmd).and_return("error msg")