[build] SKIP_SPECS env rename wasn't aligned here

Author: kares

Rakefile

@@ -165,7 +165,7 @@ end
 
 desc "Build the jruby-rack-#{GEM_VERSION}.gem"
 task :gem => [target_jar, target_jruby_rack, target_jruby_rack_version] do
-  Rake::Task['spec'].invoke unless ENV['SKIP_SPEC'] == 'true'
+  Rake::Task['spec'].invoke unless ENV['SKIP_SPECS'] == 'true'
   cp FileList["History.md", "LICENSE.txt", "README.md"], "target/gem"
   cp target_jar, "target/gem/lib"
   if (jars = FileList["target/gem/lib/*.jar"].to_a).size > 1