Fix broken YAML parsing on later Rubies with Psych >=4.0

YAML.load is now interpreted as YAML.safe_load, which breaks where the
YAML file contains aliases. If we can assume our yaml files are
trusted (since this a development tool), we can check for the presence
of YAML.unsafe_load and use it instead if it exists.

test/rakefile_helper.rb

@@ -4,11 +4,11 @@
 #   [Released under MIT License. Please refer to license.txt for details]
 # ==========================================
 
-require 'yaml'
 require 'fileutils'
 require_relative '../auto/unity_test_summary'
 require_relative '../auto/generate_test_runner'
 require_relative '../auto/colour_reporter'
+require_relative '../auto/yaml_helper'
 
 module RakefileHelpers
   C_EXTENSION = '.c'.freeze
@@ -16,7 +16,7 @@ module RakefileHelpers
     return if $configured
 
     $cfg_file = "targets/#{config_file}" unless config_file =~ /[\\|\/]/
-    $cfg = YAML.load(File.read($cfg_file))
+    $cfg = YamlHelper.load_file($cfg_file)
     $colour_output = false unless $cfg['colour']
     $configured = true if config_file != DEFAULT_CONFIG_FILE
   end