Fix body encoding

# verification
 - [ ] `./samples/tomcat_mgr_login.rb --url http://<metasploitable>:8180/manager/html --user tomcat --password tomcat`
  verify output: "LOGIN SUCCESSFUL! (tomcat:tomcat)"
 - [ ] `./samples/rails_json_yaml_scanner.rb http://<vulnerable rails server>/`
   verify output: "Probe Response Codes were 200 , 200 , 500"