bump requirements

requirements_for_test.txt

@@ -1,14 +1,14 @@
 -r requirements.txt
 flake8==3.5.0
 moto==1.3.3
-pytest==3.6.3
+pytest==3.7.1
 pytest-env==0.6.2
 pytest-mock==1.10.0
 pytest-cov==2.5.1
-pytest-xdist==1.22.2
+pytest-xdist==1.22.5
 coveralls==1.3.0
 freezegun==0.3.10
-requests-mock==1.5.0
+requests-mock==1.5.2
 # optional requirements for jsonschema
 strict-rfc3339==0.7
-rfc3987==1.3.7
+rfc3987==1.3.8