node: add without-completion option

Closes Homebrew/homebrew#26691.

Signed-off-by: Mike McQuaid <mike@mikemcquaid.com>

Formula/node.rb

@@ -44,6 +44,7 @@ class Node < Formula
 
   option 'enable-debug', 'Build with debugger hooks'
   option 'without-npm', 'npm will not be installed'
+  option 'without-completion', 'npm bash completion will not be installed'
 
   depends_on NpmNotInstalled unless build.without? 'npm'
   depends_on :python
@@ -72,8 +73,10 @@ class Node < Formula
         end
       end
 
-      # install bash completion
-      bash_completion.install lib/"node_modules/npm/lib/utils/completion.sh" => 'npm'
+      if build.with? "completion"
+        bash_completion.install_symlink \
+          lib/"node_modules/npm/lib/utils/completion.sh" => "npm"
+      end
     end
   end