Scheduled weekly dependency update for week 19 (#124)

* Update ipython from 6.3.0 to 6.4.0

* Update mypy from 0.580 to 0.600

* Update pexpect from 4.4.0 to 4.5.0

* Update pycodestyle from 2.3.1 to 2.4.0

* Update python-dateutil from 2.7.2 to 2.7.3

* Update pytz from 2018.3 to 2018.4

* Update sphinx from 1.7.2 to 1.7.4

* Update tox from 2.9.1 to 3.0.0

requirements/constraints.txt

@@ -14,36 +14,36 @@ flake8==3.5.0
 freezegun==0.3.10
 imagesize==1.0.0
 ipdb==0.11
-ipython==6.3.0
+ipython==6.4.0
 ipython-genutils==0.2.0
 Jinja2==2.10
 -e git+git@github.com:kobinpy/kobin.git@5184a9f6e0b448b41b300d1182a8552398e70a1e#egg=kobin
 MarkupSafe==1.0
 mccabe==0.6.1
-mypy==0.580
+mypy==0.600
 packaging==17.1
-pexpect==4.4.0
+pexpect==4.5.0
 pickleshare==0.7.4
 pkginfo==1.4.2
 pluggy==0.6.0
 prompt-toolkit==1.0.15
 ptyprocess==0.5.2
 py==1.5.3
-pycodestyle==2.3.1
+pycodestyle==2.4.0
 pyflakes==1.6.0
 Pygments==2.2.0
 pyparsing==2.2.0
-python-dateutil==2.7.2
-pytz==2018.3
+python-dateutil==2.7.3
+pytz==2018.4
 requests==2.18.4
 requests-toolbelt==0.8.0
 simplegeneric==0.8.1
 six==1.11.0
 snowballstemmer==1.2.1
 solar-theme==1.3.3
-Sphinx==1.7.2
+Sphinx==1.7.4
 sphinx-intl==0.9.11
-tox==2.9.1
+tox==3.0.0
 traitlets==4.3.2
 twine==1.11.0
 typed-ast==1.1.0