Revert Python 3.7 upgrade

.appveyor.yml

@@ -2,6 +2,8 @@ environment:
   global:
     RANDOM_SEED: 0
   matrix:
+    - PYTHON_MAJOR: 3
+      PYTHON_MINOR: 6
     - PYTHON_MAJOR: 3
       PYTHON_MINOR: 7
 

.travis.yml

@@ -1,7 +1,10 @@
-dist: xenial
-
 language: python
-python: 3.7
+matrix:
+  include:
+    - python: 3.6
+    - python: 3.7
+      dist: xenial
+      sudo: true
 
 cache:
   pip: true

Pipfile

@@ -6,22 +6,22 @@ name = "pypi"
 
 [requires]
 
-python_version = "3.7"
+python_version = "3" # TODO: Pin Python minor version after upgrade to 3.7
 
 [packages]
 
 # Flask
-Flask = "~=1.0.2"
-Flask-API = "~=1.1"
-Flask-CORS = "~=3.0.7"
-Flask-Caching = "~=1.6.0"
+Flask = "~=1.0"
+Flask-API = "~=1.0"
+Flask-CORS = "~=3.0.3"
+Flask-Caching = "*"
 Flask-Script = "~=2.0.6"
 
 # Utilities
 background = "*"
 markdown = "~=3.0.1"
 minilog = "*"
-pillow = "~=6.0.0"
+pillow = "~=4.1.1"
 profanityfilter = "~=2.0.5"
 pymdown-extensions = "<6"
 requests = "~=2.20.0"