Fix javadoc error on Java 11

[felixbarny]

Prerequisite for #1236

[codecov-commenter]

Codecov Report

Merging #1237 into master will decrease coverage by 0.01%.
The diff coverage is n/a.

@@             Coverage Diff              @@
##             master    #1237      +/-   ##
============================================
- Coverage     59.36%   59.34%   -0.02%     
  Complexity       87       87              
============================================
  Files           354      354              
  Lines         16270    16270              
  Branches       2269     2269              
============================================
- Hits           9658     9655       -3     
- Misses         5953     5958       +5     
+ Partials        659      657       -2     

Impacted Files	Coverage Δ	Complexity Δ
...pm/agent/profiler/asyncprofiler/AsyncProfiler.java	60.46% <0.00%> (-4.66%)	0.00% <0.00%> (ø%)
...o/elastic/apm/agent/profiler/SamplingProfiler.java	71.57% <0.00%> (-0.26%)	0.00% <0.00%> (ø%)

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[ghost]

💚 Build Succeeded

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Build stats

• Build Cause: [Pull request #1237 opened]

• Start Time: 2020-06-16T11:09:41.445+0000

• Duration: 37 min 3 sec

Test stats 🧪

Test	Results
Failed	0
Passed	1379
Skipped	11
Total	1390

[eyalkoren]

That's all it took? Nice!

[SylvainJuge]

For the record, switching to java11 from java 10 for build also requires to add <detectJavaApiLink>false</detectJavaApiLink> (e988686) to make it work, otherwise we still get the following error:

Exit code: 1 - javadoc: error - The code being documented uses packages in the unnamed module, but the packages defined in https://docs.oracle.com/en/java/javase/11/docs/api/ are in named modules.