fix(plugin-http): http.url attribute

[OlivierAlbertini]

closes #579

Short description of the changes

• add assertion in tests
• fix copy/paste error

[codecov-io]

Codecov Report

Merging #580 into master will increase coverage by 0.1%.
The diff coverage is 100%.

@@            Coverage Diff            @@
##           master     #580     +/-   ##
=========================================
+ Coverage   90.43%   90.54%   +0.1%     
=========================================
  Files         154      155      +1     
  Lines        7924     8025    +101     
  Branches      697      703      +6     
=========================================
+ Hits         7166     7266    +100     
- Misses        758      759      +1

Impacted Files	Coverage Δ
packages/opentelemetry-plugin-http/src/utils.ts	100% <100%> (ø)	⬆️
...opentelemetry-plugin-http/test/utils/assertSpan.ts	100% <100%> (ø)	⬆️
...kages/opentelemetry-metrics/test/mocks/Exporter.ts	66.66% <0%> (-33.34%)	⬇️
packages/opentelemetry-plugin-mysql/src/utils.ts	90.9% <0%> (-4.55%)	⬇️
...res/opentelemetry-plugin-pg/test/assertionUtils.ts	96.29% <0%> (-3.71%)	⬇️
...entelemetry-exporter-jaeger/test/transform.test.ts	100% <0%> (ø)	⬆️
...ges/opentelemetry-exporter-zipkin/src/transform.ts	100% <0%> (ø)	⬆️
...telemetry-plugin-grpc/test/utils/assertionUtils.ts	100% <0%> (ø)	⬆️
.../opentelemetry-exporter-zipkin/test/zipkin.test.ts	100% <0%> (ø)	⬆️
...try-node/test/instrumentation/PluginLoader.test.ts	100% <0%> (ø)	⬆️
... and 9 more