s/lck/syncObject/g

[reyang]

Fixes #1083 (comment).

Changes

Please provide a brief description of the changes here. Update the
CHANGELOG.md for non-trivial changes.

For significant contributions please make sure you have completed the following items:

• Design discussion issue #
• Changes in public API reviewed

[codecov]

Codecov Report

Merging #1084 into master will not change coverage.
The diff coverage is 50.00%.

@@           Coverage Diff           @@
##           master    #1084   +/-   ##
=======================================
  Coverage   76.59%   76.59%           
=======================================
  Files         224      224           
  Lines        6165     6165           
=======================================
  Hits         4722     4722           
  Misses       1443     1443           

Impacted Files	Coverage Δ
...y.Exporter.ZPages/ZPagesExporterStatsHttpServer.cs	0.00% <0.00%> (ø)
...enTelemetry/Trace/SimpleExportActivityProcessor.cs	0.00% <0.00%> (ø)
....Prometheus/PrometheusExporterMetricsHttpServer.cs	74.50% <100.00%> (ø)
src/OpenTelemetry/Metrics/MeterProviderSdk.cs	75.00% <100.00%> (ø)