Fix compile on ESP-IDF 4.4.3

[elliotmatson]

I was seeing this issue in ESP-IDF, this fixed it

[polaco1782]

I think a better approach would be use snprintf instead of disable warnings, like this:

snprintf(_key, sizeof(_key), "%s", key);
snprintf(_value, sizeof(_value), "%s", value);

This would enforce \0 truncation if the source string is bigger than destination. It works the same way as strncpy, but it wont throw compiler warnings

[ayushsharma82]

Using @polaco1782 suggestion with #154