gem loading benchmark needs to have the in-fork require fixed also

benchmarks/library_gem_loading.rb

@@ -21,7 +21,7 @@ def benchmark_gem_loading
       $LOAD_PATH.unshift(lib) unless $LOAD_PATH.include?(lib)
 
       VALIDATE_BENCHMARK_MODE = #{VALIDATE_BENCHMARK_MODE}
-      require 'benchmark/ips'
+      require_relative 'benchmarks_helper'
 
       Benchmark.ips do |x|
         # Gem loading is quite slower than the other microbenchmarks