Jenkins: Update dependencies (#3116)

tests/jenkins/requirements.txt

@@ -1,7 +1,7 @@
 # pyup: ignore file
-mozlog==3.5
+mozlog==3.7
 PyPOM==1.2.0
-pytest==3.3.1
+pytest==3.3.2
 pytest-metadata==1.5.1
 pytest-selenium==1.11.3
-pytest-xdist==1.20.1
+pytest-xdist==1.21.0