fixed TestLatencyStats() wrong check

[filipecosta90]

This PR fixes an added issue on #652 (comment).

check of failure

$ TEST_REDIS7_URI=redis://127.0.0.1:6379 go test exporter/*.go --test.run TestLatencyStats* -test.v
=== RUN   TestLatencyStats
    info_test.go:135: didn't find aalatency_percentiles_usec
--- FAIL: TestLatencyStats (0.06s)
FAIL
FAIL    command-line-arguments  0.067s
FAIL

check of fix:

$ TEST_REDIS7_URI=redis://127.0.0.1:6379 go test exporter/*.go --test.run TestLatencyStats* -test.v
=== RUN   TestLatencyStats
--- PASS: TestLatencyStats (0.06s)
PASS
ok      command-line-arguments  0.061s

[codecov]

Codecov Report

Merging #653 (2385975) into master (29d12ac) will increase coverage by 0.07%.
The diff coverage is 89.89%.

@@            Coverage Diff             @@
##           master     #653      +/-   ##
==========================================
+ Coverage   88.17%   88.24%   +0.07%     
==========================================
  Files          16       16              
  Lines        1826     1922      +96     
==========================================
+ Hits         1610     1696      +86     
- Misses        145      152       +7     
- Partials       71       74       +3     

Impacted Files	Coverage Δ
exporter/metrics.go	90.90% <75.00%> (-3.54%)	⬇️
exporter/info.go	95.81% <91.86%> (-1.18%)	⬇️
exporter/exporter.go	92.17% <100.00%> (+0.01%)	⬆️

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[oliver006]

Thank you!