Scheduled weekly dependency update for week 29 (#85)

* Update decorator from 4.0.11 to 4.1.1

* Update mypy from 0.511 to 0.520

* Update python-dateutil from 2.6.0 to 2.6.1

requirements/constraints.txt

@@ -7,7 +7,7 @@ click==6.7
 clint==0.5.1
 coverage==4.4.1
 coveralls==1.1
-decorator==4.0.11
+decorator==4.1.1
 docopt==0.6.2
 docutils==0.13.1
 flake8==3.3.0
@@ -20,7 +20,7 @@ Jinja2==2.9.6
 -e git+git@github.com:kobinpy/kobin.git@5184a9f6e0b448b41b300d1182a8552398e70a1e#egg=kobin
 MarkupSafe==1.0
 mccabe==0.6.1
-mypy==0.511
+mypy==0.520
 packaging==16.8
 pexpect==4.2.1
 pickleshare==0.7.4
@@ -33,7 +33,7 @@ pycodestyle==2.3.1
 pyflakes==1.5.0
 Pygments==2.2.0
 pyparsing==2.2.0
-python-dateutil==2.6.0
+python-dateutil==2.6.1
 pytz==2017.2
 requests==2.18.1
 requests-toolbelt==0.8.0