Bump mozlog from 4.0 to 4.1 (#360)

Bumps [mozlog](https://wiki.mozilla.org/Auto-tools/Projects/Mozbase) from 4.0 to 4.1.
2019-06-09 08:48:20 -07:00 · 2019-06-09 08:48:20 -07:00 · baa570887c
--- a/requirements/py27-tests.txt
+++ b/requirements/py27-tests.txt
@ -1,5 +1,5 @@
 mock==3.0.5
-mozlog==4.0
+mozlog==4.1
 pyfxa==0.7.1
 pypom==2.2.0
 pytest==4.5.0