Update defaults for Python 3 apps on Heroku

Also update our documentation and CHANGELOG for this version of the
buildpack.

CHANGELOG.md

 # Python Buildpack Changelog
 
+# 136
+
+Upgrade to 3.6.6 and support 3.7.0 on all runtimes.
+
 # 135
 
 Upgrade Pipenv to v2018.5.18.

README.md

@@ -23,7 +23,7 @@ Deploying a Python application couldn't be easier:
     $ git push heroku master
     …
     -----> Python app detected
-    -----> Installing python-3.6.5
+    -----> Installing python-3.6.6
     -----> Installing pip
     -----> Installing requirements with Pipenv 2018.5.18…
            ...
@@ -58,5 +58,6 @@ Or, with a `runtime.txt` file:
 
 Runtime options include:
 
-- `python-3.6.5`
+- `python-3.7.0`
+- `python-3.6.6`
 - `python-2.7.15`

bin/compile

@@ -49,8 +49,8 @@ export VENDOR_URL
 # These variables are used to specify which versions of Python to install by default,
 # as well as prompt the user to upgrade if they are using an un–supported version.
 # Note: When 3.7 lands, I recommend switching to LATEST_36 and LATEST_37.
-DEFAULT_PYTHON_VERSION="python-3.6.5"
-LATEST_3="python-3.6.5"
+DEFAULT_PYTHON_VERSION="python-3.6.6"
+LATEST_3="python-3.6.6"
 LATEST_2="python-2.7.15"
 
 # Which stack is used (for binary downloading), if none is provided (e.g. outside of Heroku)?

test/run

@@ -12,7 +12,7 @@ testPipenvLock() {
 
 testPipenvVersion() {
   compile "pipenv-version"
-  assertCaptured "3.6.5"
+  assertCaptured "3.6.6"
   assertCapturedSuccess
 }
 
@@ -83,7 +83,7 @@ testPython2() {
 
 testPython3() {
   compile "python3"
-  assertCaptured "python-3.6.5"
+  assertCaptured "python-3.6.6"
   assertCapturedSuccess
 }