Update Minimum Required Versions in setup.mustache

Set `certifi` to be not older than `2017.4.17` (it's the minimum version required by popular `requests` package)
Set `python-dateutil` minimum version to `2.1` (it's also minimum version required by `botocore` package)
Bump `urllib3` minimum required version to `1.23` as there were known vulnerabilities in lesser versions
PyUp Safety DB https://pyupio.github.io/safety-db/ (look for urllib3)
Snyk Vulnerability DB https://snyk.io/vuln/search?q=urllib3&type=pip

modules/swagger-codegen/src/main/resources/python/setup.mustache

@@ -16,7 +16,13 @@ VERSION = "{{packageVersion}}"
 # prerequisite: setuptools
 # http://pypi.python.org/pypi/setuptools
 
-REQUIRES = ["urllib3 >= 1.15", "six >= 1.10", "certifi", "python-dateutil"]
+REQUIRES = [
+    "certifi>=2017.4.17",
+    "python-dateutil>=2.1",
+    "six>=1.10",
+    "urllib3>=1.23"
+]
+
 {{#asyncio}}
 REQUIRES.append("aiohttp")
 {{/asyncio}}