Frozen-string-literal fixes in eval'd code.

The pragma comment doesn't pick up these uses because the code is eval'd on the fly.

cucumber.yml

@@ -1,9 +1,9 @@
 <%
 cucumber_pro_opts = ENV['ENABLE_CUCUMBER_PRO'] ? "--format Cucumber::Pro --out /dev/null" : ""
-std_opts = "--format progress features -r features --strict #{cucumber_pro_opts}"
+std_opts = "--format progress features -r features --strict #{cucumber_pro_opts}".dup
 std_opts << " --tags ~@wip-jruby" if defined?(JRUBY_VERSION)
 
-wip_opts = "--color -r features"
+wip_opts = "--color -r features".dup
 wip_opts << " --tags @wip" if !defined?(JRUBY_VERSION)
 wip_opts << " --tags @wip,@wip-jruby" if defined?(JRUBY_VERSION)
 %>

lib/cucumber/term/ansicolor.rb

@@ -56,7 +56,7 @@ def self.coloring=(val)
       ATTRIBUTES.each do |c, v|
         eval %Q{
             def #{c}(string = nil)
-              result = ''
+              result = String.new
               result << "\e[#{v}m" if Cucumber::Term::ANSIColor.coloring?
               if block_given?
                 result << yield