Use safe nav operator when calling RailsGuides::Generator.new

Use String for direction of RailsGuides::Generator

guides/rails_guides.rb

@@ -26,5 +26,5 @@ RailsGuides::Generator.new(
   only:      env_value["ONLY"],
   kindle:    env_flag["KINDLE"],
   language:  env_value["GUIDES_LANGUAGE"],
-  direction: env_value["DIRECTION"].to_sym
+  direction: env_value["DIRECTION"]
 ).generate

guides/rails_guides/generator.rb

@@ -17,7 +17,7 @@ module RailsGuides
   class Generator
     GUIDES_RE = /\.(?:erb|md)\z/
 
-    def initialize(edge:, version:, all:, only:, kindle:, language:, direction: :ltr)
+    def initialize(edge:, version:, all:, only:, kindle:, language:, direction: "ltr")
       @edge      = edge
       @version   = version
       @all       = all
@@ -118,7 +118,7 @@ module RailsGuides
       def copy_assets
         FileUtils.cp_r(Dir.glob("#{@guides_dir}/assets/*"), @output_dir)
 
-        if @direction == :rtl
+        if @direction == "rtl"
           overwrite_css_with_right_to_left_direction
         end
       end