Fix for symbol detection when nested method

When nested method as identifer detected,
@lex_state is :EXPR_MID and it becomes :EXPR_END.
However, in ":" token processing,
TkSYMBEG is generated
only when @lex_state is not :EXPR_END.
So symbol for nested method becomes TkCOLON
as distinct from TkSYMBEG.
This commit fixes the behavior.

Author: aycabta

lib/rdoc/ruby_lex.rb

@@ -1073,7 +1073,7 @@ def identify_identifier
         token.concat getc
       end
     elsif @lex_state == :EXPR_BEG || @lex_state == :EXPR_DOT ||
-          @lex_state == :EXPR_ARG
+          @lex_state == :EXPR_ARG || @lex_state == :EXPR_MID
       @lex_state = :EXPR_ARG
     else
       @lex_state = :EXPR_END