Fix regexp literal with :EXPR_END in oneliner

Regexp literal is detected by what @lex_state is :EXPR_BEG or :EXPR_MID.
But when regexp literal is after method name in oneliner,
@lex_state is :EXPR_END and the regexp literal becomes broken tokens.
This commit fixes it.

Author: aycabta

lib/rdoc/parser/ruby.rb

@@ -1502,6 +1502,7 @@ def parse_method_or_yield_parameters(method = nil,
       end
       tk = get_tk
     end
+    @scanner.first_in_method_statement = true
 
     get_tkread_clean(/\s+/, ' ')
   end

lib/rdoc/ruby_lex.rb

@@ -45,6 +45,7 @@ class Error < RDoc::Error
 
   attr_accessor :continue
   attr_accessor :lex_state
+  attr_accessor :first_in_method_statement
   attr_reader :reader
 
   class << self
@@ -112,6 +113,7 @@ def initialize(content, options)
     @indent_stack = []
     @lex_state = :EXPR_BEG
     @space_seen = false
+    @first_in_method_statement = false
 
     @continue = false
     @line = ""
@@ -352,6 +354,7 @@ def token
       begin
         tk = @OP.match(self)
         @space_seen = tk.kind_of?(TkSPACE)
+        @first_in_method_statement = false if !@space_seen && @first_in_method_statement
       rescue SyntaxError => e
         raise Error, "syntax error: #{e.message}" if
           @exception_on_syntax_error
@@ -727,7 +730,7 @@ def lex_int2
       if :EXPR_FNAME == @lex_state or :EXPR_DOT == @lex_state
         @lex_state = :EXPR_ARG
         Token(TkId, op)
-      elsif @lex_state == :EXPR_BEG || @lex_state == :EXPR_MID
+      elsif @lex_state == :EXPR_BEG || @lex_state == :EXPR_MID || @first_in_method_statement
         identify_string(op)
       elsif peek(0) == '='
         getc