Fix utils.js to replace 'en-uk' with 'en_GB' for supported language

[saideepd]

Hello @meetDeveloper ,

The language code for English (UK) as per the utils.js file is 'en-uk', but any query to the API with 'en-uk' as language code results in 404 response code.

Bu, I noticed that there was a closed Issue #50 where the support for English (UK) was added and the language code mentioned is 'en_GB'. And querying the API with 'en_GB' works perfectly fine.

Can the utils.js be updated to have 'en_GB' instead of 'en-uk'?

https://github.com/meetDeveloper/freeDictionaryAPI/blob/9e9c12c32afd7e8b4eebfbdf7e53f334f37676fb/modules/utils.js#L13