Install flake8 for development.

requires/development.txt

@@ -1,6 +1,7 @@
 -rinstallation.txt
 -rtesting.txt
 coverage==4.4.2
+flake8==3.5.0
 sphinx==1.5.6
 sphinxcontrib-httpdomain==1.5.0
 tox==1.9.2

sprockets/http/runner.py

@@ -131,7 +131,7 @@ class Runner(object):
 
         try:
             self.application.start(iol)
-        except:
+        except Exception:
             self.logger.exception('application terminated during start, '
                                   'exiting')
             sys.exit(70)