[requires.io] dependency update

Author: requires

requirements.txt

@@ -14,7 +14,7 @@ dodgy==0.1.9
 Flask==1.0.2
 github3.py==1.3.0
 inlineplz==0.46.8
-isort==4.3.7
+isort==4.3.8
 itsdangerous==1.1.0
 Jinja2==2.10               # via flask
 lazy-object-proxy==1.3.1