Fixing small std::string conversion warnings during the build process:
```
AmqpManager.cpp:40:30: use of overloaded operator '=' is ambiguous (with operand types 'AMQP::AssociativeFieldProxy' (aka 'FieldProxy<AMQP::Table, basic_string<char, char_traits<char>, allocator<char>>>') and 'const size_t' (aka 'const unsigned long'))
[build] arguments["x-message-ttl"] = AMQP_MESSAGE_TTL;
```