Update PG versions. Drop PG 9

Signed-off-by: Andrew-Chen-Wang <acwangpython@gmail.com>

README.rst

@@ -177,11 +177,10 @@ Answer the prompts with your own desired options_. For example::
     use_heroku [n]: y
     use_compressor [n]: y
     Select postgresql_version:
-    1 - 12.3
-    2 - 11.8
-    3 - 10.8
-    4 - 9.6
-    5 - 9.5
+    1 - 13.2
+    2 - 12.6
+    3 - 11.11
+    4 - 10.16
     Choose from 1, 2, 3, 4, 5 [1]: 1
     Select js_task_runner:
     1 - None

cookiecutter.json

@@ -18,11 +18,10 @@
   "use_pycharm": "n",
   "use_docker": "n",
   "postgresql_version": [
-    "12.3",
-    "11.8",
-    "10.8",
-    "9.6",
-    "9.5"
+    "13.2",
+    "12.6",
+    "11.11",
+    "10.16"
   ],
   "js_task_runner": [
     "None",

tests/test_cookiecutter_generation.py

@@ -37,11 +37,10 @@ SUPPORTED_COMBINATIONS = [
     {"use_pycharm": "n"},
     {"use_docker": "y"},
     {"use_docker": "n"},
-    {"postgresql_version": "12.3"},
-    {"postgresql_version": "11.8"},
-    {"postgresql_version": "10.8"},
-    {"postgresql_version": "9.6"},
-    {"postgresql_version": "9.5"},
+    {"postgresql_version": "13.2"},
+    {"postgresql_version": "12.6"},
+    {"postgresql_version": "11.11"},
+    {"postgresql_version": "10.16"},
     {"cloud_provider": "AWS", "use_whitenoise": "y"},
     {"cloud_provider": "AWS", "use_whitenoise": "n"},
     {"cloud_provider": "GCP", "use_whitenoise": "y"},