Add fallback when loading lang file

[necrophidia]

Description

The lang files in the lang folder existed in the package, but when retrieved, it will search for the lang folder in the working directory (which is good, especially if you wanted to do some customization for the translations).
This pull-request is intended to add a fallback logic for retrieving the lang file.

Motivation and Context

This is a possible action item for #58 and #54.
Although, you could just copy the lang folder or any lang file you desire to solve the issue.

How Has This Been Tested?

I've added a unit-test to cover the case, but can only cater for negative test-case.
Instead, I've tested at my local by pushing the changes into my forked repo, then testing with another go file with syntax:

prevTime := time.Now().AddDate(0, 0, -3)
registeredAt := carbon.NewCarbon(prevTime)
currentTime := carbon.NewCarbon(time.Now())

difference, err := registeredAt.DiffForHumans(currentTime, false, false, false)
if err != nil {
log.Println(err.Error())
}

log.Println(difference)

Approach

If the working directory does not have the lang file, it will check the downloaded/installed directory of the package from GoPath, then using the lang file from there.

[codecov]

Codecov Report

Merging #67 (e86314f) into master (ce063dd) will increase coverage by 0.94%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master      #67      +/-   ##
==========================================
+ Coverage   89.11%   90.06%   +0.94%     
==========================================
  Files           3        3              
  Lines         634      634              
==========================================
+ Hits          565      571       +6     
+ Misses         44       39       -5     
+ Partials       25       24       -1     

Impacted Files	Coverage Δ
carbon.go	91.13% <0.00%> (+0.66%)	⬆️
translator.go	65.51% <0.00%> (+6.89%)	⬆️

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[rntdrts]

Hey @necrophidia!

Thank you for your contribution! I'm sorry for the delay...

I've taken a look at the PR and it seems good to go!

[necrophidia]

no worries, @rntdrts :)
thank you for the review.

What can I do so we can merge this pull request?

[rntdrts]

no worries, @rntdrts :) thank you for the review.

What can I do so we can merge this pull request?

I'm gonna ask for one more review from someone on the team and after that, we can merge it! 🚀

[necrophidia]

nice.. thank you @rntdrts 🙏

[sardyy]

LGTM 🚀