Scheduled weekly dependency update for week 36 (#91)

* Update pluggy from 0.4.0 to 0.5.1

* Update tox from 2.7.0 to 2.8.1

* Update wsgi-lineprof from 0.3.0 to 0.4.0

requirements/constraints.txt

@@ -25,7 +25,7 @@ packaging==16.8
 pexpect==4.2.1
 pickleshare==0.7.4
 pkginfo==1.4.1
-pluggy==0.4.0
+pluggy==0.5.1
 prompt-toolkit==1.0.15
 ptyprocess==0.5.2
 py==1.4.34
@@ -43,12 +43,12 @@ snowballstemmer==1.2.1
 solar-theme==1.3.3
 Sphinx==1.6.3
 sphinx-intl==0.9.9
-tox==2.7.0
+tox==2.8.1
 traitlets==4.3.2
 twine==1.9.1
 typed-ast==1.1.0
 virtualenv==15.1.0
 wcwidth==0.1.7
-wsgi-lineprof==0.3.0
+wsgi-lineprof==0.4.0
 wsgi-static-middleware==0.1.2
 wsgicli==0.4.0