Update ruby scripts to use 'File.exist?'

Signed-off-by: Danila Fedorin <danila.fedorin@gmail.com>

agda.rb

@@ -23,7 +23,7 @@ class AgdaContext
     return @file_infos[file] if @file_infos.include? file
 
     @file_infos[file] = line_infos = {}
-    unless File.exists?(file)
+    unless File.exist?(file)
       return line_infos
     end
 

analyze.rb

@@ -43,7 +43,7 @@ files.each do |file|
   tags = []
   group = 1
   draft = false
-  next unless File.exists?(file)
+  next unless File.exist?(file)
   value = File.size(file)
   url = file.gsub(/^content/, "https://danilafe.com").delete_suffix("/index.md").delete_suffix(".md")
   File.readlines(file).each do |l|

build-agda-html.rb

@@ -26,7 +26,7 @@ files = ARGV
 code_paths = Dir.entries(root_path).select do |f|
   File.directory?(File.join(root_path, f)) and f != '.' and f != '..'
 end.to_set
-code_paths += JSON.parse(File.read(data_file)).keys if File.exists? data_file
+code_paths += JSON.parse(File.read(data_file)).keys if File.exist? data_file
 # Extending code_paths from submodules.json means that nested Agda modules
 # have their root dir correctly set.