scope the node path check

Since the anvil service which Travis uses is built using node and
anvil leaks its path into the build enviroment, node is always on the
path, so `node_js_installed?` will always return true. This executes the
direct binary skipping the PATH completely.

Author: hone

lib/language_pack/ruby.rb

@@ -693,7 +693,7 @@ def node_bp_bin_path
   end
 
   def node_js_installed?
-    @node_js_installed ||= run("node -v", env: {"PATH" => "#{node_bp_bin_path}:#{ENV["PATH"]}" }) && $?.success?
+    @node_js_installed ||= run("#{node_bp_bin_path}/node -v") && $?.success?
   end
 
   def run_assets_precompile_rake_task