Fix typo in FailedNotRetryable

[tigrannajaryan]

Continuation of open-telemetry/opentelemetry-specification#243

[songy23]

LGTM but I would suggest to wait for the specs PR to be merged first.

[codecov-io]

Codecov Report

Merging #516 into master will not change coverage.
The diff coverage is 100%.

@@            Coverage Diff            @@
##             master     #516   +/-   ##
=========================================
  Coverage     79.43%   79.43%           
  Complexity      571      571           
=========================================
  Files            65       65           
  Lines          1921     1921           
  Branches        192      192           
=========================================
  Hits           1526     1526           
  Misses          338      338           
  Partials         57       57

Impacted Files	Coverage Δ	Complexity Δ
...o/opentelemetry/sdk/trace/export/SpanExporter.java	100% <100%> (ø)	0 <0> (ø)	⬇️
...ntelemetry/sdk/trace/export/MultiSpanExporter.java	100% <100%> (ø)	12 <0> (ø)	⬇️
...lemetry/sdk/trace/export/InMemorySpanExporter.java	100% <100%> (ø)	7 <0> (ø)	⬇️

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[songy23]

Should be good to merge.