Get integration tests working on python 3.8 (#7372)

* Get integration tests working on python 3.8

* Run unit tests on py38

* Update coveragercs to use coverage 4.5+ format

* remove line added to tox.ini

* update changelog

* xenial is the new travis default; no need to specify in .travis.yml

tools/dev_constraints.txt

@@ -15,7 +15,7 @@ botocore==1.12.36
 cloudflare==1.5.1
 codecov==2.0.15
 configparser==3.7.4
-coverage==4.4.2
+coverage==4.5.4
 decorator==4.1.2
 dns-lexicon==3.2.1
 dnspython==1.15.0
@@ -76,7 +76,7 @@ Sphinx==1.7.5
 sphinx-rtd-theme==0.2.4
 sphinxcontrib-websupport==1.0.1
 tldextract==2.2.0
-tox==2.9.1
+tox==3.14.0
 tqdm==4.19.4
 traitlets==4.3.2
 twine==1.11.0