[rubygems/rubygems] Fix formatting in docs

rdoc uses + for typewriter font rather than backticks.

rubygems/rubygems@be320f1e0c

lib/rubygems.rb

@@ -48,7 +48,7 @@ module Gem
 # special location and loaded on boot.
 #
 # For an example plugin, see the {Graph gem}[https://github.com/seattlerb/graph]
-# which adds a `gem graph` command.
+# which adds a <tt>gem graph</tt> command.
 #
 # == RubyGems Defaults, Packaging
 #
@@ -581,8 +581,8 @@ def self.load_path_insert_index
   end
 
   ##
-  # The number of paths in the `$LOAD_PATH` from activated gems. Used to
-  # prioritize `-I` and `ENV['RUBYLIB']` entries during `require`.
+  # The number of paths in the +$LOAD_PATH+ from activated gems. Used to
+  # prioritize +-I+ and +ENV['RUBYLIB']+ entries during +require+.
 
   def self.activated_gem_paths
     @activated_gem_paths ||= 0
@@ -1120,7 +1120,7 @@ def self.use_gemdeps(path = nil)
 
   ##
   # If the SOURCE_DATE_EPOCH environment variable is set, returns it's value.
-  # Otherwise, returns the time that `Gem.source_date_epoch_string` was
+  # Otherwise, returns the time that +Gem.source_date_epoch_string+ was
   # first called in the same format as SOURCE_DATE_EPOCH.
   #
   # NOTE(@duckinator): The implementation is a tad weird because we want to: