ruby-lex.rb: fix for label

* 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

lib/irb/ruby-lex.rb

@@ -792,7 +792,7 @@ class RubyLex
           token_c = TkSymbol2Token[trans[1]]
           @lex_state = trans[0]
         else
-          if @lex_state != EXPR_FNAME
+          if @lex_state != EXPR_FNAME and peek(0) != ':'
             if ENINDENT_CLAUSE.include?(token)
               # check for ``class = val'' etc.
               valid = true