fix typo from r38623

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@38626 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

lib/irb/context.rb

@@ -335,7 +335,7 @@ module IRB
       @inspect_mode
     end
 
-    # Obsolate method.
+    # Obsolete method.
     #
     # Can be set using the +--noreadline+ and +--readline+ command line
     # options.