Use a plugin to read data files from gem

  - jekyll-data v1.x
  - jekyll 3.5 automatically requires a theme's runtime deps
  - jekyll v3.5.0 had bugs. Hence use v3.5.1 and beyond

Rakefile

@@ -44,6 +44,7 @@ task :preview do
 
   ENV["LISTEN_GEM_DEBUGGING"] = "1"
   listener = Listen.to(
+    base.join("_data"),
     base.join("_includes"),
     base.join("_layouts"),
     base.join("_sass"),

minimal-mistakes-jekyll.gemspec

@@ -12,14 +12,15 @@ Gem::Specification.new do |spec|
   spec.metadata["plugin_type"] = "theme"
 
   spec.files                   = `git ls-files -z`.split("\x0").select do |f|
-    f.match(%r{^(assets|_(includes|layouts|sass)/|(LICENSE|README|CHANGELOG)((\.(txt|md|markdown)|$)))}i)
+    f.match(%r{^(assets|_(data|includes|layouts|sass)/|(LICENSE|README|CHANGELOG)((\.(txt|md|markdown)|$)))}i)
   end
 
-  spec.add_runtime_dependency "jekyll", "~> 3.4"
+  spec.add_runtime_dependency "jekyll", "~> 3.5", ">= 3.5.1"
   spec.add_runtime_dependency "jekyll-paginate", "~> 1.1"
   spec.add_runtime_dependency "jekyll-sitemap", "~> 1.0"
   spec.add_runtime_dependency "jekyll-gist", "~> 1.4"
   spec.add_runtime_dependency "jekyll-feed", "~> 0.9.2"
+  spec.add_runtime_dependency "jekyll-data", "~> 1.0"
   spec.add_runtime_dependency "jemoji", "~> 0.8"
 
   spec.add_development_dependency "bundler", "~> 1.12"