Fix extracting Trans component without key, but with default value

[nicegamer7]

Hi again! Just wanted to thank you for maintaining this project, and for responding so quick to my other PRs.

Why am I submitting this PR

This PR fixes a bug that causes us to extract the keys of Trans components with default values incorrectly.

Take the following example:

<Trans>
  {{ name }}
</Trans>

The above results in the key {{name}}, which is correct. However, if we add a default value, it causes us to extract the key incorrectly:

<Trans defaults="Steve">
  {{ name }}
</Trans>

The above results in a key of Steve, which isn't correct. The key shouldn't change when we provide a default value.

Does it fix an existing ticket?

Possibly fixes #249, but I'm not sure if this is the same issue that the user was describing.

Checklist

• only relevant code is changed (make a diff before you submit the PR)
• tests are included and pass: yarn test (see details here)
• documentation is changed or added

[codecov-commenter]

Codecov Report

Patch coverage: 100.00% and project coverage change: -0.01% ⚠️

Comparison is base (d64d35a) 93.94% compared to head (cdf7397) 93.94%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #871      +/-   ##
==========================================
- Coverage   93.94%   93.94%   -0.01%     
==========================================
  Files          11       11              
  Lines        1833     1832       -1     
==========================================
- Hits         1722     1721       -1     
  Misses        111      111              

Files Changed	Coverage Δ
src/lexers/jsx-lexer.js	98.45% <100.00%> (-0.01%)	⬇️

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[karellm]

Thanks for the PR, this is deployed as 8.4.0

[nicegamer7]

Thanks karellm.