[Fix] jsx-no-useless-fragments: Allow whitespace when allowExpressions is true

[benj-dobs]

Bug fix.

Problem: When react/jsx-no-useless-fragment has allowExpression set to true, the following code produces an error:

<>
  {foo ? (
    <Bar />
  ) : (
    <Baz />
  )}
</>

This PR amends the allowExpressions rule added in #3006 to allow insignificant whitespace around the expression.

[ljharb]

awesome, thanks!

[codecov-commenter]

Codecov Report

Merging #3061 (cc95a82) into master (9487a17) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #3061   +/-   ##
=======================================
  Coverage   97.42%   97.42%           
=======================================
  Files         111      111           
  Lines        7502     7506    +4     
  Branches     2755     2758    +3     
=======================================
+ Hits         7309     7313    +4     
  Misses        193      193           

Impacted Files	Coverage Δ
lib/rules/jsx-no-useless-fragment.js	98.90% <100.00%> (+0.05%)	⬆️

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