requirements: update dependencies of some packages

i.e. dependencies' dependencies.

Author: glarrain

requirements/base.txt

@@ -32,15 +32,15 @@ requests==2.21.0
 #       - idna
 #       - urllib3
 asn1crypto==0.24.0
-cachetools==3.1.0
-certifi==2018.11.29
-cffi==1.11.5
+cachetools==3.1.1
+certifi==2019.6.16
+cffi==1.12.3
 chardet==3.0.4
 google-auth-httplib2==0.0.3
-httplib2==0.12.1
+httplib2==0.13.0
 idna==2.8
 pyasn1==0.4.5
-pyasn1-modules==0.2.4
+pyasn1-modules==0.2.5
 pycparser==2.19
 rsa==4.0
 six==1.12.0