Update critical file(s) according to Chirpy v4.3.2

Gemfile

@@ -2,7 +2,7 @@
 
 source "https://rubygems.org"
 
-gem "jekyll-theme-chirpy", "~> 4.3", ">= 4.3.0"
+gem "jekyll-theme-chirpy", "~> 4.3", ">= 4.3.2"
 
 group :test do
   gem "html-proofer", "~> 3.18"

_config.yml

@@ -79,10 +79,10 @@ theme_mode:   # [light|dark]
 # will be added to all image (site avatar & posts' images) paths starting with '/'
 #
 # e.g. 'https://cdn.com'
-img_cdn: ''
+img_cdn:
 
 # the avatar on sidebar, support local or CORS resources
-avatar: ''
+avatar:
 
 # boolean type, the global switch for ToC in posts.
 toc: true