Handle TkPLUS or TkMINUS and number as TkINTEGER

For example, lexical analyser splitted
sign character and follow number
such as "-5r" to "-" and "5r", "+1.08" to "+" and "1.08".
But this "-" or "+" is a part of number and not operator.
So this Pull Request joins it.

Author: aycabta

lib/rdoc/ruby_lex.rb

@@ -376,6 +376,10 @@ def token
       else
         tk = tk1
       end
+    elsif (TkPLUS === tk or TkMINUS === tk) and peek(0) =~ /\d/ then
+      tk1 = token
+      set_token_position tk.seek, tk.line_no, tk.char_no
+      tk = Token(tk1.class, tk.text + tk1.text)
     end
     #      Tracer.off
     tk