Set correct link to APM-Server Spans.

[simitt]

The URLs in APM Server have changed for spans.

[codecov-io]

Codecov Report

Merging #124 into master will increase coverage by 0.06%.
The diff coverage is n/a.

@@             Coverage Diff              @@
##             master     #124      +/-   ##
============================================
+ Coverage     76.73%   76.79%   +0.06%     
- Complexity      950      951       +1     
============================================
  Files            99       99              
  Lines          3297     3297              
  Branches        291      291              
============================================
+ Hits           2530     2532       +2     
+ Misses          615      614       -1     
+ Partials        152      151       -1

Impacted Files	Coverage Δ	Complexity Δ
...a/co/elastic/apm/report/ReportingEventHandler.java	81.81% <0%> (+6.06%)	10% <0%> (+1%)	⬆️

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