RUBY-3393: Rename BSON tutorial page (#321)

* rename bson-v4.txt to bson.txt

* remove bson-4 reference from docs links

Author: alexbevi

docs/tutorials/bson-v4.txt renamed to docs/tutorials/bson.txt

@@ -1,10 +1,10 @@
-.. https://www.mongodb.com/docs/ecosystem/tutorial/ruby-bson-tutorial-4-0/
+.. https://www.mongodb.com/docs/ecosystem/tutorial/ruby-bson-tutorial/
 
-.. _ruby-bson-tutorial-4-0:
+.. _ruby-bson-tutorial:
 
-*****************
-BSON 4.x Tutorial
-*****************
+*************
+BSON Tutorial
+*************
 
 .. default-domain:: mongodb
 
@@ -26,13 +26,13 @@ To install the gem manually:
 
 .. code-block:: sh
 
-    gem install bson -v '~> 4.0'
+    gem install bson
 
 To install the gem with bundler, include the following in your ``Gemfile``:
 
 .. code-block:: ruby
 
-    gem 'bson', '~> 4.0'
+    gem 'bson'
 
 The BSON library is compatible with MRI >= 2.5 and JRuby >= 9.2.