Update ddtrace to 0.19.0

[pyup-bot]

This PR updates ddtrace from 0.18.0 to 0.19.0.

Changelog

0.19.0

With `0.19.0` we have decided to disable the tracing of `dbapi2` `fetchone()`/`fetchmany()`/`fetchall()` methods by default.

This change effects all integrations which rely on the `dbapi2` API, including `psycopg2`, `mysql`, `mysqldb`, `pymysql`, and `sqlite3`.

We have introduced this change to reduce the noise added to traces from having these methods (mostly `fetchone()`) traced by default.

With `fetchone()` enabled the traces received can get very large for large result sets, the resulting traces either become difficult to read or become too large causing issues when flushing to the trace agent, potentially causing traces to be dropped.

To re-enable the tracing of these methods you can either configure via the environment variable `DD_DBAPI2_TRACE_FETCH_METHODS=true` or manually via:

python
from ddtrace import config
config.dbapi2.trace_fetch_methods = True


Changes
Bugs
[dbapi2] disable fetchone/fetchmany/fetchall tracing by default (780)
[opentracing] Fixing context provider imports for scope manager (771 -- thanks Maximilien-R)

Enhancements
[tests] test python setup.py sdist and twine check on build (782)
[core] Add API to configure Trace Search (781)
[core] Enable priority sampling by default (774)

Read the [full changeset](https://github.com/DataDog/dd-trace-py/compare/v0.18.0...v0.19.0) and the [release milestone](https://github.com/DataDog/dd-trace-py/milestone/32?closed=1).

Links

• PyPI: https://pypi.org/project/ddtrace
• Changelog: https://pyup.io/changelogs/ddtrace/
• Repo: https://github.com/DataDog/dd-trace-py

[coveralls]

Pull Request Test Coverage Report for Build 462

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 44.62%

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Totals
Change from base Build 459:	0.0%
Covered Lines:	311
Relevant Lines:	697

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💛 - Coveralls

[coveralls]

Pull Request Test Coverage Report for Build 462

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 44.62%

---

Totals
Change from base Build 459:	0.0%
Covered Lines:	311
Relevant Lines:	697

---

💛 - Coveralls