* lib/irb/ruby-lex.rb (identify_identifier): treat identifier just
  followed by a colon as a lable.  this is not a precise solution
  but enough for the time being.  [ruby-core:78526] [Bug #13012]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@57027 b2dd03c8-39d4-4d8f-98ff-823fe69b080e